(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Biodiversity Heritage Library | Children's Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "1978 Yearbook of Astronomy"

00 

< 

m 

> 

CD 
O 

o 
o 

-n 

§ 

O 



5 

o 

o 
o 

m 



TO 

o' 



o 

s 





£4.50 

In UK only 




Yea* 
Astronomy 

There is a major change in this edition. 
The Editor, writing with the authority of 
personal knowledge, says; "Astronomy is 
a truly international subject; and now that 
the Yearbooks are read and used all over 
the world, it is time to include southern star 
maps. These have been prepared by 
Dr. Porter, whose monthly notes are now 
equally relevant to both hemispheres." 
Thus observers will be able to know what 
is happening on the other side even though 
they can't see. 

The usual essential information on 
planets, eclipses, comets, and meteors is 
included, while the lists of double stars, 
variables, clusters, and nebulae have been 
extended, 

The article section is as varied as ever, 
with illustrations and diagrams as applicable, 
Our contributors include old and new 
friends, as the following list shows: 

Observatory Fitments F. R. Spry 

The Earth and the Moon R. Maddison 

The Zodiacal Light J. C. D. Marsh 

Craters on Mercury 

and Mars S. Miyamoto 

The Atmosphere of Mars: 

Past, Present and Future G. E. Hunt 

Neutron Stars J. Bell Burnell 

Extragalactic Nomenclature 

- A Simple Guide S. Mitton 

What's New in the 

Local Group Heather Couper 

Interstellar and 

Intergalactic Matter I. Nicolson 

Recent Events in 

Astronomy Patrick Moore 



1978 

Yearbook of Astronomy 



1978 

Yearbook of 
Astronomy 

PATRICK MOORE 




Sidgwick & Jackson Limited 

LONDON 



First Published in Great Britain 1977 

Copyright © 1977 by Sidgwick and Jackson Limited 

Published in Great Britain by 

Sidgwick and Jackson Limited 

1 Tavistock Chambers, Bloomsbury Way 

London WC1A 2SG 

0.283.98392.2 (Hard) 
0.283.98393.0 (Limp) 



Phototypesetting by Print Origination 

Bootle, Merseyside L20 6NS 

and 

Printed in Great Britain 

by Biddies of Guildford 



Contents 

Editor's Foreword ■ 7 
Preface • 9 

PART ONE: EVENTS OF 1978 
Notes on the Star Charts • 13 
Northern Star Charts • 16 
Southern Star Charts • 42 
The Planets and the Ecliptic • 68 
Phases of the Moon, 1978 • 73 
The Planets in 1978 • 74 
Events of 1978 • 76 
Monthly Notes • 77 
Eclipses in 1978 • 100' 
Occultations in 1978 101 
Comets in 1978 • 102 
Meteors in 1978 • 105 
Minor Planets in 1978 ■ 106 
Some Events of 1979 ■ 108 



CONTENTS 

PART TWO: ARTICLE SECTION 
Observatory Fitments: F. R. Spry -111 

The Earth and the Moon: R. Maddison • 114 

The Zodiacal Light: /. C. D. Marsh • 130 

Craters on Mercury and Mars: 5. Miyamoto • 135 

The Atmosphere of Mars: Past, Present, and 
Future: G. E. Hunt • 144 

Neutron Stars: S. J. Bell Burnell • 165 

Extragalactic Nomenclature — A Simple Guide: 
S. Mitton ■ 174 

What's New in the Local Group: H. Couper- 186 

Interstellar and Intergalactic Matter: /. Nicolson • 198 

Recent Advances in Astronomy: Patrick Moore -210 

PART THREE: MISCELLANEOUS 

Some Interesting Telescopic Variable Stars -217 

Some Interesting Double Stars -218 

Some Interesting Clusters and Nebulae • 220 

Some Recent Books • 221 

Our Contributors • 223 

Astronomical Societies in Great Britain • 225 

6 



Editor's Foreword 

Those who have read the Yearbooks over the past fifteen years 
will notice a major change in this new version. Ever since 1962, 
when the series began, the main emphasis has been upon the 
Northern Hemisphere, and only northern monthly charts have 
been included. However, astronomy is a truly international 
subject; and now that the Yearbooks are read and used all over 
the world, it is time to include southern star-maps. These have 
been prepared by Dr Porter, whose monthly notes are now 
equally relevant to both hemispheres. The lists of double stars, 
variables, clusters and nebulae have also been extended. 

As usual, the article section includes 'something for every- 
body', ranging from observatory hints to the movements of the 
Moon, the local group of galaxies, and neutron stars — the 
latter written by Dr Jocelyn Bell Burnell, who was the first to 
identify these remarkable objects now known as pulsars. There 
is also an important review article, by Dr Garry Hunt, concern- 
ing the new findings about the atmosphere of Mars. This kind 
of article would have seemed very futuristic in 1962, before the 
first successful Mars probe had been launched. 

PATRICK MOORE 

Selsey, 1977 



Preface 

New readers will find that all the information in this Yearbook 
is given in diagrammatic or descriptive form; the positions of 
the planets may easily be found on the specially designed star 
charts, while the monthly notes describe the movements of the 
planets and give details of other astronomical phenomena 
visible in both the northern and southern hemispheres. Two 
sets of star charts are provided. The Northern Charts (pp. 16 to 
41) are designed for use in latitude 52 degrees north, but may be 
used without alteration throughout the British Isles, and 
(except in the case of eclipses and occultations) in other 
countries of similar north latitude. The Southern Charts (pp. 
42 to 67) are drawn for latitude 35 degrees south, and are 
suitable for use in South Africa, Australia and New Zealand, 
and other stations in approximately the same south latitude. 
The reader who needs more detailed information will find 
Norton's Star At las (Gall and Inglis) an invaluable guide, while 
more precise positions of the planets and their satellites, 
together with predictions of occultations, meteor showers, and 
periodic comets may be found in the Handbook of the British 
Astronomical Association. A somewhat similar publication is 
the Observer's Handbook of the Royal Astronomical Society 
of Canada, and readers will also find details of forthcoming 
events given in the American Sky and Telescope. This monthly 
publication also produces a special occultation supplement 
giving predictions for the United States and Canada. 

Important Note 

The times given on the star charts and in the Monthly Notes 
are generally given as local times, using the 24-hour clock, the 
day beginning at midnight. The times of a few events (e.g. 



PREFACE 

eclipses) are given in Greenwich Mean Time (G.M.T.), which is 
related to local time by the formula 

Local Mean Time = G. M.T. — west longitude. 

In practice, small differences of longitude are ignored, and the 
observer will use local clock time, which will be the appropriate 
Standard (or Zone) Time. As the formula indicates, places in 
west longitude will have a Standard Time slow on G.M.T., 
while places in east longitude will have Standard Times fast on 
G.M.T. As examples we have: 

Standard Time in 

New Zealand 
Victoria; N.S.W. 
Western Australia 
South Africa 
British Isles 
Eastern S.T. 
Central S.T. 

If Summer Time is in use, the clocks will have been advanced 
by one hour, and this hour must be subtracted from the clock 
time to give Standard Time. 

In Great Britain and N. Ireland, Summer Time will be in 
force in 1978 from 19 March 02 h until 22 October 02 h G.M.T. 



G.M.T. 


+ 


12 hours 


G.M.T. 


+ 


10 hours 


G.M.T. 


+ 


8 hours 


G.M.T. 


+ 


2 hours 


G.M.T. 






G.M.T. 


— 


5 hours 


G.M.T. 


— 


6 hours, etc, 



10 



PART ONE 

Events of 1978 

MONTHLY CHARTS and ASTRONOMICAL 
PHENOMENA 



Notes on the Star Charts 

The stars, together with the Sun, Moon and planets seem to be 
set on the surface of the celestial sphere, which appears to 
rotate about the Earth from east to west. Since it is impossible 
to represent a curved surface accurately on a plane, any kind of 
star map is bound to contain some form of distortion. But it is 
well known that the eye can endure some kinds of distortion 
better than others, and it is particularly true that the eye is most 
sensitive to deviations from the vertical and horizontal. For 
this reason the star charts given in this volume have been 
designed to give a true representation of vertical and horizontal 
lines, whatever may be the resulting distortion in the shape of a 
constellation figure. It will be found that the amount of 
distortion is, in general, quite small, and is only obvious in the 
case of large constellations such as Leo and Pegasus, when 
these appear at the top of the charts, and so are drawn out 
sideways. 

The charts show all stars down to the fourth magnitude, 
together with a number of fainter stars which are necessary to 
define the shape of a constellation. There is no standard system 
for representing the outlines of the constellations, and triangles 
and other simple figures have been used to give outlines which 
are easy to follow with the naked eye. The names of the 
constellations are given, together with the proper names of the 
brighter stars. The apparent magnitudes of the stars are 
indicated roughly by using four different sizes of dots, the 
larger dots representing the bright stars. 

The two sets of star charts are similar in design. At each 
opening there is a group of four charts which give a complete 

13 



1978 YEARBOOK OF ASTRONOMY 

coverage of the sky up to an altitude of 62Vi degrees; there are 
twelve such groups to cover the entire year. In the Northern 
Charts (for 52 degrees north) the upper two charts show the 
southern sky, south being at the centre and east on the left. The 
coverage is from 10 degrees north of east (top left) to 10 degrees 
north of west (top right). The two lower charts show the 
northern sky from 10 degrees south of west (lower left) to 10 
degrees south of east (lower right). There is thus an overlap east 
and west. 

Conversely, in the Southern Charts (for 35 degrees south) 
the upper two charts show the northern sky, with north at the 
centre and east on the right. The two lower charts show the 
southern sky, with south at the centre and east on the left. The 
coverage and overlap is the same on both sets of charts. 

Because the sidereal day is shorter than the solar day, the 
stars appear to rise and set about four minutes earlier each day, 
and this amounts to two hours in a month. Hence the twelve 
groups of charts in each set are sufficient to give the appearance 
of the sky throughout the day at intervals of two hours, or at 
the same time of night at monthly intervals throughout the 
year. The actual range of dates and times when the stars on the 
charts are visible is indicated at the top of each page. Each 
group is numbered in bold type, and the number to be used for 
any given month and time is summarised in the following table: 



Local Time 


18h 


20h 


22h 


Oh 


2h 


4h 


6h 


January 


11 


12 


1 


2 


3 


4 


5 


February 


12 


1 


2 


3 


4 


5 


6 


March 


1 


2 


3 


4 


5 


6 


7 


April 


2 


3 


4 


5 


6 


7 


8 


May 


3 


4 


5 


6 


7 


8 


9 


June 


4 


5 


6 


7 


8 


9 


10 


July 


5 


6 


7 


8 


9 


10 


11 


August 


6 


7 


8 


9 


10 


11 


12 


September 


7 


8 


9 


10 


11 


12 


1 


October 


8 


9 


10 


11 


12 


1 


2 


November 


9 


10 


11 


12 


1 


2 


3 


December 


10 


11 


12 


1 


2 


3 


4 



14 



NOTES ON THE STAR CHARTS 

The charts are drawn to scale, the horizontal measurements, 
marked at every 10 degrees, giving the azimuths (or true 
bearings) measured from the north round through east (90 
degrees), south (180 degrees), and west (270 degrees). The 
vertical measurements, similarly marked, give the altitudes of 
the stars up to 62 V2 degrees. Estimates of altitude and azimuth 
made from these charts will necessarily be mere approxima- 
tions, since no observer will be exactly at the adopted latitude, 
or at the stated time, but they will serve for the identification of 
stars and planets. 

The ecliptic is drawn as a broken line on which longitude is 
marked at every 10 degrees; the positions of the planets are 
then easily found by reference to the table on page 74. It will be 
noticed that on the southern charts the ecliptic may reach an 
altitude in excess of 62 x /i degrees on star charts 5 to 9. The 
continuation of the broken line will be found on the charts of 
overhead stars. 

There is a curious illusion that stars at an altitude of 60 
degrees or more are actually overhead, and the beginner may 
often feel that he is leaning over backwards in trying to see 
them. These overhead stars are given separately on the pages 
immediately following the main star charts. The entire year is 
covered at one opening, each of the four maps showing the 
overhead stars at times which correspond to those of three of 
the main star charts. The position of the zenith is indicated by a 
cross, and this cross marks the centre of a circle which is 35 
degrees from the zenith; there is thus a small overlap with the 
main charts. 

The broken line leading from the north (on the Northern 
Charts) or from the south (on the Southern Charts) is num- 
bered to indicate the corresponding main chart. Thus on page 
40 the N-S line numbered 6 is to be regarded as an extension of 
the centre (south) line of chart 6 on pages 26 and 27, and at the 
top of these pages are printed the dates and times which are 
appropriate. Similarly, on page 66, the S-N line numbered 10 
connects with the north line of the upper charts on page 60. 

The overhead stars are plotted as maps on a conical projec- 
tion, and the scale is rather smaller than that of the main charts. 

15 



1978 YEARBOOK OF ASTRONOMY 



1L 



October 6 at 5 
November 6 at 3 h 
December 6 at 1 

January 6 at 23 h 



October 21 at 4 

November 21 at 2 

December 21 at midnight 

January 21 at 22 



February 6 at 21 February 21 at 



20 n 



60"- 



30"- 



Poltux 



100 



LYNX 



.••' 110 GEMINI 



. .-■• K0 

v »'' CANCER 
•'130 




CANIS 
/• MINOR 
# Procyon 



N40 



V-"* / 

LEO ^9 Regulus • 

' ,50 ^ HYDRA 



."170 



Sirius • — . # 



CANIS 
MAJOR 



1 1 1 r; 1 r 

E 120° 



-i r 



150° 



»'■ 



A PERSEUS 



ANDROMEDA 




/CASSIOPEIA 

> 



• 1 

/CEPHEUS* 



Polaris • 
\ 



/ % 



\ 



\ 



Deneb 



-"V 



■CYGNUS 



300" 



TT — r 

330 



W-" 



16 



NORTHERN STAR CHARTS 



October 6 at 5 h 

November 6 at 3 h 

December 6 at l h 

January 6 at 23 h 

February 6 at 21 h 



October 21 at 4 

November 21 at 2 h 

December 21 at midnight 

January 21 at 22 h 

February 21 at 20 h 



1R 



-5?.... 



/ 



-•■■.. 70* 



/ 



Algol. 



,f PERSEUS 



-60° 



V 



A Idebaran^ \ 



V 



JP\m ORION 

i \ • 

ltRigel 



""•-, 60 * Pleiades 

TAURUS "'•. 

• '••. .50 



/TRIAN- 

l/l 



I GULUM 



-.40 



<<1 

LEPUS 



T \. 



\ 



* ARIES 



,30 



ERIDANUS / 



, CETUS 



/ \ 



>; 20 



PISCES 



— r- 1 1 1 1 1 1- 

210* 240° W 



30° 



URSA 
\ MINOR 


/ 


/ 


• 

URSA ,'\ 


• 

LYNX N » 




/ 
/ 

• 


MAJOR ,C-'" 


/• 


^^ DRACO / 


/ 


I 


• 


•— 


-'^ 




I 

• 


• 


/LEO 


<> 






S COMA 


y- / 


\ KERCULES 

\ X , 


• ' 


"~*\ BOOTES 
\ 

• 


\ BERENICES 

• 


*170 


' 


'. 


■ I • 1 


.'. ' ' 


"I" 



-60° 



-30° 



30* 



60' 



17 



1978 YEARBOOK OF ASTRONOMY 



2L 



November 6 at 5 
December 6 at 3 
January 6 at 1 
February 6 at 23 h 
March 6 at 21 h 



November 21 at 4 

December 21 at 2 

January 21 at midnight 



February 21 at 
March 21 at 



22 n 
20 h 



60*- 



30*- 



URSA"- — -, 
MAJOR ^ 



/ COMA 
/ BERENICES 




'"" 120 



140 



■&0 CANCER 



HYDRA 



*170 



• v VIRGO /£'l80 



r r 



/ /' 



190 



r 



-T 

120* 



150* 



60- 



30- 



'i Captlta 



CASSIOPEIA 




Marls | 




Otntb . 



CYGNUS\ „ 
-^ 



18 



November 6 at 5 h 

December 6 at 3 h 

January 6 at l h 

February 6 at 23 h 

March 6 at 21 h 



NORTHERN STAR CHARTS 

November 21 at 4 h 

December 21 at 2 h 

January 21 at midnight | 2R 



February 21 at 
March 21 at 



22" 
20 h 



"V 



110 



GEMINI 



>•— 1 



-60' 



100 



90 



AURIGA /"' 



CANIS MillOR 
^Procyon 



80 • 



Betelgeuse • — . • 
\l 

/ N 



ORION 



TAURUS '-4 

70 - 

* r 
>t/defcara/i» s ? 



/ 



!■ Pleiades 



60 ' 



SiriusQ^ 
CANIS / "" 
MAJOR / 

•4L 






50" 



'Rigel 



N 

LEPUS • 



ERIDANUS 

— -•s. 



\ 



-. 40 \ 

\ • 



.' CETUS 30 V . 



210" 



240° 



1^ 
W 



-30" 



-«o* 



URSA 
\, MINOR 



/ 



•; 



• URSA MAJOR 



/ 



\^ DRACO 



\ 



\ 



COMA 
BERENICES 



BOOTES 



HERCULES 



Vega 

'• 

— r~ 



1 — V 

30* 



•^, w /(rctorus 

i CORONA 
..,• BOREALIS # 



l\ 



-i r— 

60* 



30* 



19 



1978 YEARBOOK OF ASTRONOMY 



3L 



December 6 at 5 
January 6 at 3 
February 6 at 1 
March 6 at 23 h 
April 6 at 21 h 



December 21 at 4. 

January 21 at 2 

February 21 at midnight 
March 21 at 22 h 



April 21 at 



20 n 



(.0"- 



30* 



\ 



LEO 



COMA 

BERENICES 



_\ 



Regulusl 
n*» 

..-•' 150 



BOOTES 



'Arcturus 



"\ VIRGO y<*' 



•' V 170 



•\. 




•-«> CORVUS / HYDRA 



x'220 I 

1 " 1 I ' 1 1 1 1 ' I 

1 ' 120* 150» S 



60*- 



30 



AURIGA 



Polaris i 




v*° / / 



80*. 
TAURUS 

Aldtbaran 



s 



\t '••. ^pietadts 

• 60"<. 



50' 



• PERSEUS 

/ "W \ 



i- 



N 

EUS 

i 
i 

\ 



CEPHEUS 
I 



CASSIOPEIA 






ANDROMEDA 



n r 

W 



-i 1 1 r- 

300° 330' 



-i r 



20 



NORTHERN STAR CHARTS 



December 6 at 5 

January 6 at 3 h 

February 6 at l h 

March 6 at 23 h 

April 6 at 21 h 



December 21 at 4 

January 21 at 2 h 

February 21 at midnight 

March 21 at 22 h 

April 21 at 20 h 



3R 



• — 

LEO 



-60° 



Pollux _ 



,0 Castor 



U0 






•' — \ 

• +... • \ « \ 

CANCER WO ... \ \ GEMINI 

™> -k. \ f< 



HYDRA 



CANIS MINOR 
Procyon 



80' 



ORION 



t r 



canis s ir us 

MAJOR / \ 



Betetgeuse 

/ N ^ Atdebaranq • 
/ / \ **i 

•• .. 

Rigel \ 



■30" 



- r; 

210 



T I 



240° 




-SO* 



Arcturus 



SERPENS 



-30" 



21 



1978 YEARBOOK OF ASTRONOMY 



4L 



January 6 at 5 h 

February 6 at 3 h 

March 6 at l h 

April 6 at 23 h 

May 6 at 21 h 



January 21 at 4 h 

February 21 at 2 h 

March 21 at midnight 

April 21 at 22 h 



May 21 at 



20 n 



60"- 



BOOTES 



' ircturus 



'■ CORONA 
,«" BOREALIS 



VIRGO 



io-- 



p- — •' 

,i HERCULES 



SERPENS 



190 



,-'/ 2 °° 
■' %Spica 



4 210 



LIBRA 



V 



OPHIUCHUS 






.*220 



-• x 230 



CORVUS 



HYDRA 



a 



/ 



.S240 



120° 



T 



~ 1 — 
150' 



80- 



30* 



Polaris ' 



P °" "!—• Castor 



V.I \ GEMINI 

1,0 V-. v 






X- 



AURIGA 
— • Capetta 



CASSIOPEIA 

\ 



90 \ 



y 7\ PERSEUS 



^ 



80 •- 



Bttelgeuse 



/ /* 



70' 



i. *L 



300* 



330* 



22 



NORTHERN STAR CHARTS 



January 6 at 5 h 

February 6 at 3 

March 6 at l h 

April 6 at 23 h 

May 6 at 21 h 



January 21 at 4 

February 21 at 2 h 

March 21 at midnight 

April 21 at 22 h 

May 21 at 20 h 



4R 




"T 



/Regulus 

" oV x"w<; 



LYNX 



130--.. 
CANCER 



Pollux 



Castor - 



HYDRA 



^V- # 



120'"'--. • 1 • \ 
••-. GEMINI 



no'-. 



CANIS MINOR 

• — * 
Procyon 



I "I . 

210* 



BtMg*use9^ 



■60" 



-30* 



240° 



I I 

W 



URSA 
MINOR 



y*~" 



V^l 



DRACO 



"V 



\CEPHEUS 



\ 



Den*b 



/ CYGNI 



CYGNUS 



30* 



t^Vega 
V LYRA 



~£~ 



HERCULES 



/ 




■60° 



-30* 



23 



1978 YEARBOOK OF ASTRONOMY 



5L 



January 6 at 7 
February 6 at 5 
March 6 at 3 h 
April 6 at l h 
May 6 at 23 h 



January 21 at 6 

February 21 at 4 

March 21 at 2 h 

April 21 at midnight 
May 21 at 22 h 



60' 



30* 




CORONA 
BOREALIS 



Arcturus 



/ 




.' SERPENS 

. \ 



• OPHIUCHUS 






•n. libra 



•'"220 






Altair 



AQUILA 



/ 



^^-« • ••'/A SCORPIUS 



• " 260 • stares 



120 



150° 



60- 



30*- 



V- 



I 
URSA J MAJOR 

! 

i 



• LYNX 



LEO 



13&"*-.. Mtux 
CANCER*"*/. 
120 



Castor 



> 



w 



;x-. • \ • \ 

'**"•• 1 \GEMINI 

"° v* ^ 

• \ioo--V 

»t r " 



/ AURIGA 

Capella 




J** 



PERSEUS 




300° 



I & I 



330* 



24 



NORTHERN STAR CHARTS 



January 6 at 7 h 

February 6 at 5 h 

March 6 at 3 h 

April 6 at l h 

May 6 at 23 h 



January 21 at 6 

February 21 at 4 h 

March 21 at 2 h 

April 21 at midnight 

May 21 at 22 h 



5R 





m 


URSA 


\\ 


• 

• 




% MAJOR 

• 

• 




A 








/ 


*"^-w "X 






/ I VIRGO 


""'" 160"-- 


\.^ — -. 
<°) \ 

■--J-fRegulus 
150 V"---,. 

\ HO ""-.. 

130 


i 

• 




. m J*i CORVUS 


HYDRA 


/*— »s 




\ y 


' X -W 


-• 


i 


\^ 






. • 



-60' 



■30* 



I 1 ;-- | | j— | | r" 

210° 2«0° W 



^Polaris 



I 




-60* 



CEPHEUS\» 



/ 



CASSIOPEIA 



Dene6 i 



:/ 



HERCULES'^ 

y 

,9 Vega •- 

N^/'LYRA 



• \ CYGNUS 



-A 



SAGITTA 



Altaic 

delphinus* Vn . aquila/ 



-30* 



-l r 

30" 



I 
60' 



25 



1978 YEARBOOK OF ASTRONOMY 



6L 



March 6 at 5 h 

April 6 at 3 h 

May 6 at l h 

June 6 at 23 h 

July 6 at 21 h 



March 21 at 4" 

April 21 at 2 h 

May 21 at midnight 



June 21 at 
July 21 at 



22" 
20 h 



60- 



30'- 



• • Vega 
IYRA X » 



«"" 



HERCULES 



CYGNUS 



SAGITTA 



• OPHIUCHUS 



DELPHINUS * 



VAltair 

/ACLUILA 



SERPENS 



/ 




250 
260.--** // 

• W 

SCORPIUS.* 

• 



LYNX 



160 """*•« 'Regulus 
150 V-...^ 

N . M0 



/ AURIGA 
i Capella 



Castor 



130" 



Potlux^- 



300* 



330* 



26 



NORTHERN STAR CHARTS 



March 6 at 5 h 

April 6 at 3 h 

May 6 at l h 

June 6 at 23 h 

July 6 at 21 h 



March 21 at 4 h 

April 21 at 2 h 

May 21 at midnight 
June 21 at 22 h 



July 21 at 



20 n 



6R 



\ 



BOOTES 



-60° 



Arcturus 



* SERPENS 





VIRGO 



\ . ■ 



/ 



\,/ / CORVUS 



180 "■••/- 

170 ""is6---..V 




16- r 



240* 



1^ 
W 



-30" 



. URSA 
/ MINOR 

t Polaris 




Deneb^ 



CYGNUS 



CASSIOPEIA * 



/ PERSEUS • 



DELPHI NUS 



; ' ■ e — ■ — r - 



/A 



PEGASUS 



— -•' 



— I — 
60° 



■60" 



30° 



27 



1978 YEARBOOK OF ASTRONOMY 



7L 



May 6 at 3 h 
June 6 at 1 
July 6 at 23* 
August 6 at 21 
September 6 at 19 h 



May 21 at 2 

June 21 at midnight 
July 21 at 22 h 

August 21 at 20* 

September 21 at 18 



60°- 



CYGNUS • 



SAGITTA 



30*- X-A 



DEIPHINUS 



Ultalr 



y 



< AQUILA 



. \ 



PEGASUS 



• /; 



,»S . . 280 • 
300 ?^?..."«..»+-™- 



.>.' AQUARIUS 3li 

■^" J 330 ^^i^CAPRICORNUS 

^* / 340 ....-•+ " r * 

'• / 350 ...;'*- SAGITTARIUS 

" V \ 



&<± 



t r 



120° 



t r 



-i — 

150' 



T 



60*- 



30- 



\ 



X 



BOOTES 



URSA *\ 
MINOR 



'V 



V 



^. DRACO 
\ 



y 




i\ 



COMA 
BERENICES 



/ 

\ 



/\ URSA \ 
/ \ MAJOR \ 

' ** * 

/ \\ • 

/ W > 



VIRGO 



1 r 

W 



y\ LEO 



J" LYNX 



300* 



1 r 



- 1 — 

330° 



t r 



28 



NORTHERN STAR CHARTS 



May 6 at 3 h 

June 6 at l h 

July 6 at 23" 

August 6 at 21 h 

September 6 at 19 h 



May 21 at 2 h 

June 21 at midnight 

July 21 at 22 h 

August 21 at 20 h 

September 21 at 18 h 



7R 



* 

• 


\ ... 


— • ■ 


/J3- 


CORONA S" 
BOREALIS y^ 
->. • BOOTES 


n— 

* OPHIUCHUS 

• 


jl _ Arcturus 

f • 

/ SERPENS 

• /COMA 


V° 2S0 ,.„ 


'" i -S&-— — i 

Sp/ca# -1?.°\ 


Antares^Z^J 

SCORPIUS /• • 

/ 

• 


> 1 1 


I l 1 1 


1 1 



■60* 



-30" 




-30« 



29 



1978 YEARBOOK OF ASTRONOMY 



8L 



July 6 at l h 
August 6 at 23 
September 6 at 21 h September 21 at 



October 6 at 19 



November 6 at 17 November 21 at 



July 21 at midnight 

August 21 at 22 h 

20 h 

18 h 

16 h 



October 21 at 



60°- 




pisces y • u -•;» 4- 

V 350 /\ 340 330 -^—310— -;+J 

.-*...-'.—' ■"" / \ CAPRICORNU5 300 

30 T / . .' I 



120° 



ISO" 



T 7 " 

\ 

DRACO 



60" 



30- 



HERCULES 



CORONA 
BOREALIS 



\ 



BOOTES 
Arcturus 



coma * 
• BERENICES 



'V 



•-#^' URSA *n 

MINOR 



\ 



-/ 



? v URSA \ 
i \ MAJOR *• 
I "•«> \- 



330 # 



300* 



30 



NORTHERN STAR CHARTS 



July 6 at l h 

August 6 at 23 h 

September 6 at 21 h 

October 6 at 19 h 

November 6 at 17 h 



July 21 at midnight 

August 21 at 22 h 

September 21 at 20 h 

October 21 at 18 h 

November 21 at 16 h 



8R 



SA6ITTA 



jJMair 






HERCULES 



AQUILA 



\ 



OPH1UCHUS 



290 



\ 



SERPENS 



: *-*..,280 m 

SAGITTARIUS />• * ""*•->? 

1 f 



CORONA 
BOREALIS 



Arcturus 



■W 



-30* 



250 



210* 



2*0° 



I 
W 



-JO' 



% Polaris 



CASSIOPEIA \ 



Capelta 



AURI3A 





TRIANGULUM 

", PISCES 

• — • 

• ARIES i /... 

...•-!« • / r 

-. Pleiades 



.-•-■'^o 



40 



'1/ 



IF 



IF 



T 



I 



31 



1978 YEARBOOK OF ASTRONOMY 



9L 



August 6 at 1 

September 6 at 23 h 

October 6 at 21 h 

November 6 at 19 h 

December 6 at 17 h 



August 21 at midnight 
September 21 at 22 h 

October 21 at 20* 

November 21 at 18 

December 21 at 16 




30- 



PEGASUS 



• — • 
ARIES 



*0 



. | ..\.-- 2 ^-"'"l( 
'30 ? / 



.- - -i 



350 



<- 



AQUARIUS 

,340 "• — , 
330' 



50 



CETUS 



/ 



\, 



Fomathaut 



120° 



150° 



60"- 



30°- 



LYRA 
^5« 0Vega 



/ 

•<7\ 



RACO / /VURSA 

/ // MINOR 



N. 



CORONA 









BOOTES 



> URSA 
; MAJOR 



SERPENS 



Arcturus 

-r« — i — 

300° 



330° 



32 



August 6 at l h 



NORTHERN STAR CHARTS 



August 21 at midnight 



September 6 at 23 September 21 at 



October 6 at 21" 



October 21 at 



November 6 at 19 November 21 at 
December 6 at 17 h December 21 at 



22 h 
20 h 
18 h 
16 h 



9R 



LYRA 



DELPHINUS 

i 



^« Vega 



V 



*> SAGITTA 



\ 



AQUILA 



-60° 



'•-.. 320 

o-... 






HERCULES 



3ICN... CAPRICORN 
306'-... 

296"--. • 



I Polaris 



URSA 
MAJOR 



V- 



'*/ 



us • ••~~-^l o 



OPHIUCHUS 



'•.,280 



• • 



SERPENS 



210* 



2*0° 



A 



•30* 



•r CASSIOPEIA 



-60* 



ANDROMEDA ^ 




PERSEUS •-« • £ 

• Atg5l*-y' TRIAN6ULUM 



\ 



CapeUa 



V 



AURIGA 



A \L 



X 

^ \ J P/»/otfes <0 



60 
..••6*0 TAURUS 



• M Mdtbaran 



v 90 



30* 



"JF 



-30° 



33 



1978 YEARBOOK OF ASTRONOMY 



10L 



August 6 at 3* 
September 6 at I 
October 6 at 23 h 
November 6 at 21 h 



August 21 at 2 

September 21 at midnight 
October 21 at 22 h 



November 21 at 



December 6 at 19 December 21 at 



20" 
18 h 



60«- 



. PERSEUS 



ARIES 



30"- 



^-/ 



60 



Pleiades 
i ..»••■•■ 
50 



/ PISCES 

•..../ ..^-.r— — 

30 f 20 i 



70 .--'■""' TAURUS 
V" *• \ 

*Atdebaran 



10 



CETUS 



t 




ERIDANUS 



//VoRlON /* "\/ I 

leeuse a^* » • 



Betelgeuse 



l r^— i r 



120* 



-i r; — r 

150* 



60*- 



• % Deneb 

/ • 

• •- 



/ 

4 CYQNUS 



• «£> • Vega 

acT-ft. LYRA 



\ 



,7m 

T ORACO I i— • 



Polaris 



/ URSA 
' MINOR 



. ^ 



Vk 



HERCULES 



/ URSA 
* MAJOR 



T 1 

300* 



^ 



jl \ 



BOOTES 



S30* 



34 



August 6 at 3 

September 6 at l h 

October 6 at 23 h 

November 6 at 21 h 

December 6 at 19 h 



NORTHERN STAR CHARTS 



August 21 at 2 h 

September 21 at midnight 

October 21 at 22 h 

November 21 at 20 h 



December 21 at 



18" 



10R 



_>*. 



PEGASUS 



N. . 



CYGNUS 






-»• 



DELPHINUS 




Y 



•'• SAGITTA 



Fomathaut 



• AQUILA 



CAPRICORNUS . 



30<K 



•30" 



210* 



- 1 

2*0° 



W 



\ URSA MAJOR 



•» 



— -J? 



If 




h«" 



\yr^ 



N 



AURIGA 



/ 70 



GEMINI 



Castors- 
Pollux «. 



X.. 



' • TAURUS 



• ..•••• X ' 00 \ 2>\ 



Bttelgtuse 



-30» 



"^ 



^ 



35 



1978 YEARBOOK OF ASTRONOMY 



HL 



September 6 at 3 

October 6 at 1* 

November 6 at 23 

December 6 at 21 

January 6 at 19 



September 21 at 2 

October 21 at midnight 
November 21 at 22 h 

December 21 at 20 

January 21 at 18 




60- 



30'- 



CEPHEUS 



• • 



Dtn*b 



~...._-4-:.--- 



Polaris , 
URSA 



»U((« m 



CYGNUS 



DELPHINUS 

t 



J MINORf 

p ^ 

J DRACo\ 

4 V.^- 



\ 



<*• 



V*ga 

LYRA 



SA6ITTA 



X 



AGUILA ^^ 



# \ 



w 



300* 



\. 



¥■ 



• ■ 

J. 



HERCULES 



330* 



■Z^I. 



36 



NORTHERN STAR CHARTS 



September 6 at 3 h 

October 6 at l h 

November 6 at 23 h 

December 6 at 21 h 

January 6 at 19 h 



September 21 at 2 h 

October 21 at midnight 

November 21 at 22 h 

December 21 at 20 h 



January 21 at 



18 n 



11R 




DELPHINUS 

» > 



Altair 



60° 



-30° 



"1 1 1 T 

210° 



' v 320 



240" 



-i r 



w 



i Polaris 



Capelta #=n*5s« 

/\ 
~>V \ AURIGA 



90, 



GEMINI 






Castor: 
Pollux 



m— .•*ioo \ 



•^ 



/ 



_j. / URSA 

•~^ ^« MAJOR 



30* 



^110 



"^LYNX 



LEO 



,.M20 
* /CANCER / 



A 



.130 



60» 



• Procyon 

l 1 

E 



SO* 



-30' 



37 



1978 YEARBOOK OF ASTRONOMY 



12L 



October 6 at 3* 
November 6 at l h 
December 6 at 23 

January 6 at 21 h 
February 6 at 19 



October 21 at 2 h 

November 21 at midnight 
December 21 at 22 

January 21 at 20 

February 21 at 18 h 



«o*- 



Castor 4 
Pollux 




V 

. 80 



l - 

70 « % 

Aldebaran9-»—' 

TAURUS 



30*- 



.•"120 



Btttlgeuse 
ORION 



CANCER .'' 
/l30 



CANIS I MINOR 
• Procyon 






\ 



/MO 

• Regulus 






Sirius 9 



/C\u pus 



HYDRA 

A 



\ CANIS 
MAJOR 



t r- 1 r 

120* 



ISO* 



60*- 



CASSIOPEIA 



URSA i 
MINOR] 



30- 



PEGASUS 



> 




«... 



1 ^r. \y 

■ i i ■ i 



300" 



»30* 



38 



NORTHERN STAR CHARTS 



October 6 at 3 h 
November 6 at l h 
December 6 at 23 h 

January 6 at 21 h 
February 6 at 19 h 



October 21 at 2 h 

November 21 at midnight 
December 21 at 22 h 

January 21 at 20 h 

February 21 at 18 h 



12R 



ANDROMEDA 




-60° 



' I r— r 

210° 



> 



DRACO 



340-. 



240° 



w 



•30" 



-60° 



S 



Castor m— 

\ 
Pollux 4 



V: 



/^ 



URSA 
MAJOR ,'* 



. LYNX 



.•130 



/ LEO v,. f 



>-. 



>140 



-| 1 T r 

30* 



. ,}< ., 



m'Regulus 
••150 



60* 



-30° 



39 



1978 YEARBOOK OF ASTRONOMY 



NORTH 




NORTH 




Northern Hemisphere Overhead Stars 



NORTHERN STAR CHARTS 



NORTH 




NORTH 




Northern Hemisphere Overhead Stars 



41 



1978 YEARBOOK OF ASTRONOMY 



1L 



October 6 at 5 h 

November 6 at 3 

December 6 at 1 

January 6 at 23 

February 6 at 21 



October 21 at 4jj 

November 21 at 2 

December 21 at midnight 
January 21 at 22 

February 21 at 20 h 



eer- 




r 

• ^ ERIDANUS 

\ / 






Fornax 
• 


r- 

f 






^ / 




30°- 


• - 

L 


— — * 

^J CETUS 

/ • 

A 


• 






ORION 



\<t^B»tal- 



geust 



50 



.^ Aldeboran 
* S? * 

_-->" "80 "" 90 

..*'-" 70 TAURUS. 
'60 •- 

i^Plttadts 



40 



/.'A' 30 ARIES * \ TJ\ 

V'",n \ •— • PERSEUS • S» 

> \ * Cam 



.AURIGA, 



10 ,- , 
a' X PISCES 



.- 

-f- 



-| 1 

300" 



* -^-v 



Capella j 



330° 



60"- 



30>- 



PYXIS 



/ 



\ False -.-'■ 
• ^Cros;** 



VOLANS, 



\ VELA / * \ CARINA* « 

/ \ * / / 



MAELEON 



HYDRA 



CRATER/* \ 



•2° 




1 



w* 

O-* •mJsca 



► CRUX 



*\ 
APUS*t 

TRIANG. 
R. 



CENTAUR US 






.__ # -<r "CIRCINUS / 



• •--_ AUSTI 



T 



150° 



42 



SOUTHERN STAR CHARTS 



October 6 at 5 h 

November 6 at 3 h 

December 6 at l h 

January 6 at 23 h 

February 6 at 21 h 



October 21 at 4 h 

November 21 at 2 h 

December 21 at midnight 

January 21 at 22 h 

February 21 at 20 h 



1R 



60"- 



MONOCEROS 



PYXIS .. 



•"CANIS 
MINOR 



3o-»**Ky-~^o. 



GEMINI 



• <** HYDRA 

V~- JM CANCER "~"^. 



-• 

V 



*Ca*tor 



-V«> • 



RtgulusiJZ 



LYNX, 



1 r 



30" 



-i r 



CRATER/ 

\^ \leo \^ 



60» 



■f-^—r 



60*- 



30*- 



./ 



\/RETlCULUM 



ERIDANUS J 



i HYDRUS V 



%Achernar 



OCTANS 



-\ 



A 



TUCANA 



\ 




•'TORNAX m - 



, \ PAVO \ | -I «'__.- 

"•-*• • \IN0US \ GRUS 



» \ 



17 



/CETUS 



-I r— 1 1 r 

210° 



<7 •' 



w, 



240° 



43 



1978 YEARBOOK OF ASTRONOMY 



2L 



November 6 at 5 
December 6 at 3 
January 6 at l h 
February 6 at 23 
March 6 at 21 h 



November 21 at 4 

December 21 at 2 h 

January 21 at midnight 

February 21 at 22 h 

March 21 at 20 h 



60»- 



LEPUS 



I 



MONOCEROS 



30«- 



/ 






Procyon 

/CANIS 
MINOR 



i ERIOANUS 

I 



• - 
\ 

s 



$ 



BetelgeusQ 



3 



-^.W- 



J-^fi S y%>« 



*-'"*> GEMInT~~*-— / 
Ald&beran ^'' Castor 

P* ,-''80 




*60 



TAURUS , 



-'50 



-W 



I \AURtGA 
Vapello 



T" 



300° 



330" 



80 9 - 



HYDRA 



.. CRATER 



•\. 



30«- 



A 

CORVUS\ 



..190 




CENTAURUS 



»-2°0, 



ISptco 
"-^210 



.VIRGO 



X220 



/ \^ ,CIRCINUS *p x 



PAVO 



120 



— I — 
150 



44 



November 6 at 5 h 

December 6 at 3 h 

January 6 at l h 

February 6 at 23 h 

March 6 at 21 h 



SOUTHERN STAR CHARTS 



November 21 at 4 h 

December 21 at 2 h 

January 21 at midnight 

February 21 at 22 h 



March 21 at 



20" 



2R 



60"- 



r 



CANCER 
- 1 ?? 



130 



30«- 



HYDRA 






•~\ 



HYDRA 



CRATER/»-"*\ 

\ i 



60»- 



30»- 




45 



1978 YEARBOOK OF ASTRONOMY 



3L 



January 6 at 3 h 

February 6 at l h 

March 6 at 23 h 

April 6 at 21 h 

May 6 at 19 h 



January 21 at 2 

February 21 at midnight 

March 21 at 22 h 

April 21 at 20 h 

May 21 at 18 h 



60*. 



30«- 




HYDRA 



• %Slrius \ 

^ MONOCEROSI 



Procyon 
I CANIS 



1*0---" 



1*9 



MINOR 



120,-' 



„.LEPUS 

A ■'. 

C I /*\ 

^» / \\ORION « 110^-' . 

\ ,' m ~* J GEMINI 

y k" so,/ 

80/ 



130. 



LEO N « 



f LYNX 



ERIDANUS 



t r 



i r 



"i r 



w 



300* 



330° 



60"- 



Imusca 



30*- 




* \ Antans SCORPIUS f A 



250 v 



^ 



120° 



^./TELESCOPIUM ^m 



150» 



46 



SOUTHERN STAR CHARTS 



January 6 at 3 h 

February 6 at l h 

March 6 at 23 h 

April 6 at 21 h 

May 6 at 19 h 



January 21 at 2 

February 21 at midnight 
March 21 at 22 h 



April 21 at 
May 21 at 



20" 
18 h 



3R 



60*- 






<. 


CRATER 


•-ZZ^n,«\ HYDRA 
" CORVUS \ 




160 

■ffRegulus 


170 










• 




/ 


VIRGO "~ v v,210 


30^ 


/• LTO # 






L 

• — 


• 




URSA I 
MAJOR ! 


V 


COMA / 
• 


• 
• 


LIBRA/ \"230- 

• — V 




- • i 


• 






-Arcturus 

/BOOTES * 




1 1 


1 


I 


i 


> 1 1 1 



30" 



60° 



60«- 



30»- 



• t \CARINA 
"^~^» \]V0LANS ^\ 

• " • \^ 


•' PI 

^QCanopus 


JPPIS 


- •— ■ 


CANIS / 

major/ 

• :/ 


\ 1 






-sPICTOR 


COLUMBA. . 


\. 




«^^ 


•— — . 


*\ / 


• 


SiriuS ~ 




\dorado 






^S 




RETICULUM 










• 


«£? 


• 




LEPUSJ 1 

m 


• 
• 

• 


• HYORUS f 

• 


v » 




i.S~\ 


drion/ x 


r? 


Achemar 

• — '-^ 




ERIDANUS i 

1 


m 


<' 


TUCANA / / 


• 




s 


.-^/ 


\ / / phoenix 


* FORNAX^ 


\ ERIDANUS 


i — r- 


• — • 
1 


1 1 


1 1 


• 
1 


1 



210° 



240° 



47 



1978 YEARBOOK OF ASTRONOMY 



4L 



February 6 at 3 h 

March 6 at l h 

April 6 at 23 h 

May 6 at 21 h 

June 6 at 19 h 



February 21 at 2 h 

March 21 at midnight 

April 21 at 22 h 

May 21 at 20 h 

June 21 at 18 h 



60«- 



30°- 



PYXIS 



PUPPIS 



CANIS 
M^JOR 

V Sirius 




1_ 



W 



60°- 




30°- 



180 



HYDRA 



J5- 



160 



/ „_ , 150/ —• 

;Regulus £ " 
/W *\ LEO 



. CANCER ^ 
±Procyon / . 



I CANIS 120,'' 
* MINOR / 



LYNX^ 



URSA 
MAJOR 
• -.. 



• 110' 
GEMINI 3 m 

m ^-7 ^ 



,Pollux 

T 



300° 



330° 



LIBRA f~ Vr'LUPUS 



\ CENTAURUS 



250' An>ar " \ • .• 



• MUSCA 

*— "TSRCINUS 

# -— , ~~?TRIANG 
,\ /AUSTR 

AHA,. V/ AP 



X 



lP jK 



260- 



SCORPIUS ^ 



,/\ 



OPHIUCHUS 



■TELESCOPIUM 

-, X \ CORONA 

* 270\ > lAUSTR. 

*-v» \ -V. 



\ 



V^PAVO 



OCTANS/ 



TUCANA 




48 



February 6 at 3 h February 21 at 2 h 

March 6 at l h March 21 at midnight 

April 6 at 23 h April 21 at 22 h 

May 6 at 21 h May 21 at 20 h 

June 6 at 19 h June 21 at 18 h 



SOUTHERN STAR CHARTS 

4R 




~'--. 220 



A>l230 "l-IBRA 

/ \ V ^«-» 



xr>- 



COMA 




• Ardurus 



SCORPIUS 



BOOTES 



250\ 






URSA 
MAJOR 



- 1 — 
30° 



CORONA 
BOREAL IS 

"1 1 — 



SERPENS 



••vJDPHIUCHUS 



60° 



T-'^-T- 



60°- 



V-A 



VELA 



\ CARINA .f>\ / PYXIS 

• \ \ 'False \_ / •-• 

|> •Cross \ # ' 



30»- 




49 



1978 YEARBOOK OF ASTRONOMY 



5L 



March 6 at 3 n 

April 6 at l h 

May 6 at 23 h 

June 6 at 21 h 

July 6 at 19 h 



March 21 at t 

April 21 at midnight 
May 21 at 22 h 



June 21 at 



20" 



60°- 



30°- 



July 21 at 18 n 

200y-" 



\ 



CRATER 



180 




170y 



\ HYDRA 



<J 




COMA' 



URSA 
MAJOR 



300° 



330° 



60°- 



^*x Arrtares 



2601^«- 



270*, 



30°- 



SCORPIUS ' 



1-V 



ARA 



I \ ^TRI 

— ••-— I k^ au: 



TfLESCOPIUM 7 

'Ci < 



TRIAN6. 
AUSTR. 



APUS 



• ~\_ # /|SAGITTARIUS .' ^USTR* 
280 K !>-• • 

/"scutum /■\ 29q ^\. 

\AQUILA '->j300 



PAVO 




y 

\ OCTANS// 

i^' .z/ 



•, TUCANA 



-% 



K 



GRUS 



Y310 



Achernor 



120° 



150° 



50 



SOUTHERN STAR CHARTS 



March 6 at 3 h 

April 6 at l h 

May 6 at 23 h 

June 6 at 21 h 

July 6 at 19 h 



March 21 at 2 h 

April 21 at midnight 



May 21 at 
June 21 at 
July 21 at 



22 n 
20 h 
18 h 



5R 



60°- 



30°- 



V 



LIBRA 



"•-*- 



SERPENS 



*^. 



OPHIUCHUS 



^Antares 
250"% SCORPIUS 

26 6\ • 



270 \ 



. BOOTES 



I x - *nr\or\Kin 



> 'CORONA 
BOREALIS 



V 




280 



/'scutum 



i\ 



OHERCULES 



AQUILA 



30° 



60" 



60*- 



30«- 



MUSCA «_ 



CRUX/J^-. 



/CENTAURUS 



\ 



CHAMAELEON 



/ • 
'CARINA 



VOLANS \/\ 



VELA 



HYDRA 



\ 




MAJOR 



<. 



240° 



"i r~ 

w 



51 



1978 YEARBOOK OF ASTRONOMY 



6L 



March 6 at 5 h 

April 6 at 3 h 

May 6 at 1* 

June 6 at 23 h 

July 6 at 21 h 



March 21 at 4 h 

April 21 at 2 h 

May 21 at midnight 

June 21 at 22 h 

July 21 at 20 h 



60 a - 



30"- 



*220 



HYDRA/ / 

^-^•\CORVUS 200 X 

/ \. .' • ,7 



SERPENS . 

/ 



/crater 
\ ,N »-— .^" ' 80 , 



,90 v— < 

/ / VIRGO 



HYDRA 



^Arcturus 



BOOTES 



CORONA 
BOREALIS 

\ 



170-t 



COMA 



160-1 




LEO 



-i 1 r 

300° 



.», — .. 



330° 



60°- 



30°- 



> ^ ~ 

./-"/SAGITTARIUS CORONA \ 

/ AIISTR / 



AUSTR./ 



Wfy/ 



\£0 


,t^. 


V 




/ 


v >290 




v 300 



f° CAPRICORNUS 



w 



INDUS 



-•.GRUS 

/ V^-« 

• •— — 




\ \i 



32o\\ PISCIS\ 

AQUARIUS \ * AUSTR | \ 

T > *^« 

Fomolhaut * 



330"; 



T 1 

120° 



\tucana 



* PHOENIX/* f' 



HYCRUS N ! 



r 



\ 



150° 



52 



SOUTHERN STAR CHARTS 



March 6 at 5 h 

April 6 at 3 h 

May 6 at l h 

June 6 at 23 h 

July 6 at 21 h 



March 21 at 4 h 

April 21 at 2 h 

May 21 at midnight 



June 21 at 
July 21 at 



22 n 
20 h 



6R 



60*- 



-.^ 



270- 



OPHIUCHUS 



\ 



. N t NSAGITTARftB 

/SCUTUM /290V 



30"- 



• • 



\ HERCULES 
.- »^ 



300f. 



-IV 



\*ga%^ 



SAGITTA^J 
LYRA \ 



.. AQUILA «s^ CAPRICORNUSX ^ 
•*Mto$r ' \ 



.DELPHINUS 



32<n 



4 .^ 



EQUULEUS 



~ 1 

30° 



60° 



60*- 



-*> 




CENTAURUS 



IARINA J • 

lY* y&f /vaA / 

/False f • -* 

/Cross \ 
f • / . \ ^ 

DORADOi I ' L -^ 

:^DR 



* , PUPPIS. 



.PYXIS 



\ 



T" 



T 
210° 



\ 



240° 




53 



1978 YEARBOOK OF ASTRONOMY 



7L 



April 6 at 5 h 

May 6 at 3 h 

June 6 at l h 

July 6 at 23 h 

August 6 at 21 h 



April 21 at 4 h 

May 21 at 2 h 

June 21 at midnight 

July 21 at 22 h 

August 21 at 20 h 



60*- 



30°-" 




OPHIUCHUS • • 




SERPENS 



/, 



HERCULES 



f*CORONA * \. . 

i BOREALIS y\ 




60°- 



Jxp 



CAPRICORNUS 



\ I 

30*- V330 



\\ / SCULPTOI 

', ^^ -./ 

- 350l AQUARIUS 



C\i 



RETICULUM 



• ; * J 

.'eridanus yS 

,-OORADC; 



120° 



ISO* 



54 



SOUTHERN STAR CHARTS 



April 6 at 5 h 

May 6 at 3 h 

June 6 at l h 

July 6 at 23" 

August 6 at 21 h 



April 21 at 4 h 

May 21 at 2 h 

June 21 at midnight 



July 21 at 
August 21 at 



22 h 
20 h 



7R 



60°- 



30°- 



\ SCUTUM 
^ V 



300 v \ 



•OPHIUCHUS 



. • 



• \ 

AQUILA »- 

<,SAGITTA 



CAPRICORNUS 



LYRA, 

9° /- 



DELPHINUS 



EQUULEUS 



Vega 1 J 



^3X) 

\\ 
330^ 

Uquarius\ 



• CYGNUS 

\ --•— • 

»^ 

. I • ' 
* #Denefc 



PEGASUS '. 



*50 



30° 



_ __* 



60° 



60°- 



30' 



TRIANG. 
AUSTR. • 



I ^CIRCINUS 



t»APUS 



OCTANS 



CHAMAE)<£ON • 






.MUSCA CRUX 



VOLANS •""^- L* * 

•^ • • • 

CARINA m /*\--J* 

* -false t VELA 

Cross /• 




55 



1978 YEARBOOK OF ASTRONOMY 



8L 



May 6 at 5 h 

June 6 at 3 h 

July 6 at l h 

August 6 at 23 h 

September 6 at 21 h 



May 21 at 4 h 

June 21 at 2 h 

July 21 at midnight 

August 21 at 22 h 

September 21 at 20 h 



60"- 



270 



SCUTUM . 



260-" 



\ 



AQUILA 



30»- 



QAntaref 

,• /250 
/ |\/SC0RPIUS 

i-2/O \ 



Attain 



1 



OPHIUCHUS , 



SAGITTA* 



»220 



LIBRA 



. SERPENS 



v_, -o 



HERCULES 



f| LYRA 
Vega 



1 1 1 — — r 

300° 



f*sam> •' 



w 



~~ i r 

330° 



W- 



\ PISCIS 
I \AUSTR. 

Fomolhaut%~~~ 



/AQUARIUS 

SCULPTOR 



30°- 



CETUS 




•Vgrus • 



/ \ 

PAVO 




/ 



< TUCANA 



V-* 



PHOENIX 



OCTANS 



Aehernar HYDRUS 



'ERIDANUS 



V 



FORNAX 



120° 



/[RETICULUM 

# ___ • VOLANS 

DORADO ^^-» 

/ PICTOR 



150° 



56 



SOUTHERN STAR CHARTS 



May 6 at 5 h 

June 6 at 3 h 

July 6 at l h 

August 6 at 23 h 

September 6 at 21 h 



May 21 at 4 h 

June 21 at 2 h 

July 21 at midnight 

August 21 at 22 h 

September 21 at 20 h 



8R 



68"- 



30«- 



320' V . 



DELPHINUS 



CYGNUS 




PISCISl \ 
AUSTRj • 

\ \ 
FomalhautQ — 



350 V 



PEGASUS 



\ 



a\ 



Den«b 



I 
30° 



i r 



60° 



\l V CETUS p 

PISCES * \ \ / 

2oV 

"i h 1— 



60°- 



~? PAVO \ 



ARA _— .• 

-• * / 
-. ^* — * 



^ SCORPIUS 



260?-- 



• T A» 



X^-^'AUSTR. "^ 250 / 

OCTANS * \ /• ^* AMant 9 s r 

\ Vapus Vs* CIRCINUS / /t\ • 

• \ * — */ \ ' 

CHAMAEttON % ^MUSCA \\ .• .• . LIBRA /\. 

*S T . ?—/<•/ « \ 230 '/\ 



7- .- > •* 



CENTAURUS < 



CARINA / 



— 1 r 

210° 



/ 



220^ 

'hydra 

210* 



-\ n~ 



2<o° 



w 



57 



1978 YEARBOOK OF ASTRONOMY 



9L 



June 6 at 5 
July 6 at 3* 
August 6 at 1 



June 21 at 4 

July 21 at 2h 

August 21 at midnight 



September 6 at 23 September 21 at 



October 6 at 21 



October 21 at 



22" 
20 h 



60°- 


\sAGITTARIUS 


,--'*3bo 


<. 




• 


• 

AQUARIUS -— ^. 




\ 


> 


^j CAPRICORNUS 










y- 


/ 












- 


-~^y 


. — • 




• 




EQUULEUS* 




y< 


'280 






/ 




• • / 






• " 






- 


K 

>270 




». 

— • 


• 


\ 


Altalr 


*\ OELPHINUS 




/ 




SCUTUM 


AQUILA 






30°- 


.'*> . 


• 


• 






**-* 






\ 




• 
• 


• 
• 




SAGITTA 


- 








• • 








CYGNUS •' 




■ 


► 


OPHIUCHUS •. 


• 






\/ / 


- 


\ 


• 


/ /* 

• • 


• 




V • • 










• * 


\*ga0m 








1 


1 


i 


1 




1 





300° 



330° 



«P- 



30°- 



/SCULPTOR 



PHOENIX 



TUCANA 



IAT— . 



.Acharnar 



ERIDANUS, 



/CETUS 



/ 



FORNAX / 



> HYDRUS , 



•^RETICULUM 



'.ERIDANUS 



1 • - 



DORADO ^-•' 



Canopus 
COLUMBA . • 




False V" 
.Cross v' # 



t— • — r 



120° 



-i r 

150° 



58 



SOUTHERN STAR CHARTS 



June 6 at 5 

July 6 at 3 h 

August 6 at l h 

September 6 at 23 h 

October 6 at 21 h 



June 21 at 4 h 

July 21 at 2h 

August 21 at midnight 

September 21 at 22 h 

October 21 at 20 h 



9R 



60°- 



30"- 




60° 



•„TRIANG. V _•__./ 



./CORONA 
TELESCOPIUM \AUSTR. 

SAGITTARIUS^ 

•— *\ / '"280 

ARA « «' y 



.iuJ^VP' 



30°- 



CIRCINUS 






! SCORPIUS •- 



X 



\./ 



•-Jmusca _ 



LUPUS 



• CRUX 



\ 



Airfares^ 



,'*\ 






OPHIUCHUS 



*"-'-•. , • , 230..' 



\ 



210° 



T 



240° 



W 



59 



1978 YEARBOOK OF ASTRONOMY 



10L 



July 6 at 5 h 

August 6 at 3 h 

September 6 at l h 

October 6 at 23 h 

November 6 at 21 h 



July 21 at 4 h 

August 21 at 2 h 

September 21 at midnight 

October 21 at 22 h 

November 21 at 20 h 



60°- 



30"- 



- ,jt 341 

• tr* ,_-- 330 

CAPRICORNUS S «•■'' 

/,-'' 320 AQUARIUS/*— »-* 

**-/' .. — — -• ' 



350 



PISCES 



300 -'' / 



,"590 



EQUULEUS 



*V 



PEGASUS 






• ' _ WAIMr 

. • AOUILA 

SCUTUM f<* 



DELPHINUS 



SAGITTA 



/ CYGNUS 



~\ r 



300° 



— i r 

330° 



60°- 



30°- 




jf HYDRUS 
RETICULUM \ _• 



DORADO 



PICTOR 



. * COLUMBA \# . V7 *"~— -— 

A ♦C^* •Cancpus N^OLANS ~ 

y \LEPUS T . \CARINA ^ 9 

• *\ ^ /• V .False V« " \ . 

i. ^* ^/XANIS \ t. m i • -— "^ \V • * * 

**6r7on . •\MAJ° f H?\ r^\ \vELaV. * •• 



- 1 — r 

E 



120° 



-\ r 

150° 



60 



SOUTHERN STAR CHARTS 



July 6 at 5 h 

August 6 at 3 h 

September 6 at l h 

October 6 at 23 h 

November 6 at 21 h 



July 21 at 4 h 

August 21 at 2 h 

September 21 at midnight 

October 21 at 22 h 

November 21 at 20 h 



10R 



60«- 



FORNAX , 



MO- 




W- 



INDUS 



30°- 



JO 
4* 





3oq, 






TELESCOPIUM C0R0NA ^ 
/ 7 'AUSTR. 
TRIANG./T /"\ARA * 



29q,-' 



•*^-^£IRCINUS i 

» ,• scorpiusN 



r\r Of 



SAGITTARIUS 



CRUX 



V \ / 

• — •*- OPHIUCHUS. 



SCUTUM 



/\. LUPUS *. \ 260> x . . • 



210° 



240° 



61 



1978 YEARBOOK OF ASTRONOMY 



liL 



August 6 at 5 

September 6 at 3 h 

October 6 at l h 

November 6 at 23 h 

December 6 at 21 h 



August 21 at 4 

September 21 at 2 h 

October 21 at midnight 
November 21 at 22 h 



December 21 at 



20" 



60*- 



CETUS 






AQUARIUS 



\ 350. *- 



340>- 



CAPRICORNUS ^ 
3CH . .** /' L^ 



/ 



>^20 



/ 



A 



V 



EQUULEUS 




PEGASUS 



ANDROMEDA 



-i r 

w 



—i 1 1 1 — 

300° 330° 



60°- 



-.^ERIDANUS 



/^LEPUS 



PICTOR \ 

/COLUMBA . . •\ > 

T %Canofub\^ 



RETICULUM 



-DORADO 



/HYDRUS 



•VOLANS 



30*- 



n^tL- * : 



Strius l _ _ 

• MAJOR ./P"^*.. *\ 

MONOCEROS V 



OARINA \p> . 

A dMAMAELEON 



canis ^/^ ,«,,«; 4 • — *\H-%l • \* 

\*\ # _# MUSCAT 






\ 



VELA 



./ PYXIS 



Procyon 



V \ •/ c 



CRUX 



- 1 r 

120° 



— t r 

150° 



62 



SOUTHERN STAR CHARTS 



August 6 at 5 

September 6 at 3 h 

October 6 at l h 

November 6 at 23 h 

December 6 at 21 h 



August 21 at 4 

September 21 at 2 

October 21 at midnight 
November 21 at 22 h 

December 21 at 20 h 



11R 



60°- 



30°- 




60»- 



30«- 



TUCANA 



n 



Fbmolhaut 



GRUS | 



INDUS 





330, 



CAPRICORNUS .' ^320 



TELESCOPtUM 



• .• VCIRCINUS 
/ 



/\ 1 tLtaourium ^-«. \ 
0*r u 



rA x 

AUSTR. 



?-. *"? > > 



SAGITTARIUS^ 



AQUARIUS 



/"290 



210° 



240° 



63 



1978 YEARBOOK OF ASTRONOMY 



12L 



September 6 at 5 

October 6 at 3 h 

November 6 at l h 

December 6 at 23 h 

January 6 at 21 h 



September 21 at 4 

October 21 at 2 h 

November 21 at midnight 

December 21 at 22 h 

January 21 at 20 h 



eo<>- 



CETUS 



30"- 



• — • 


TAURUS 


ARIES 
•-• 


Pleiades £• 

• 

PERSEUS * 




60°- 



30 c 



HYDRA 



TRIAN6. 
CRUX MS J* 

\ 



^CENTAURUS • ^Y • 



CIRCINUS 



120° 



150° 



64 



September 6 at 5 h 

October 6 at 3 h 

November 6 at l h 

December 6 at 23 h 

January 6 at 21 h 



SOUTHERN STAR CHARTS 



September 21 at 4 h 

October 21 at 2 h 

November 21 at midnight 

December 21 at 22 h 

January 21 at 20 h 



12R 



60°- 



ERIDANUS 



.— . i 



Riga) 



>f 




' ORION 



CANIS • 

• MAJOR 



30*- 



^~""*-0 Aldabaran 

TAURUS ~~ #> • 

• \ \J V 00 \ 

I \ \ \N 

AURIGA | \ GEMINI\ ^' 10 



Betelgouse 






MONOCEROS 



PUPPIS 



-Procyon 



CANIS 
MINOR 



• cop»/*j#; 



V 



Castor 



—\ — 
30° 



-J20 -• 

~V„130 

1 ^t 



*£** HYDRA 



60° 



60°- 



30°- 




SCULPTOR 



.7 -7 



PISCIS V / 

AUSTR - AQUARIU^/'' 



350 



, ARA 



CAPRICORNUS/ -'' /*"> 



210° 



240° 



W 



65 



1978 YEARBOOK OF ASTRONOMY 





Southern Hemisphere Overhead Stars 



66 



SOUTHERN STAR CHARTS 





Southern Hemisphere Overhead Stars 



67 



The Planets and the Ecliptic 

The paths of the planets about the Sun all lie close to the plane 
of the ecliptic, which is marked for us in the sky by the apparent 
path of the Sun among the stars, and is shown on the star charts 
by a broken line. The Moon and planets will always be found 
close to this line, never departing from it by more than about 7 
degrees. Thus the planets are most favourably placed for 
observation when the ecliptic is well displayed, and this means 
that it should be as high in the sky as possible. This avoids the 
difficulty of finding a clear horizon, and also overcomes the 
problem of atmospheric absorption, which greatly reduces the 
light of the stars. Thus a star at an altitude of 10 degrees suffers 
a loss of 60 per cent of its light, which corresponds to a whole 
magnitude; at an altitude of only 4 degrees, the loss may 
amount to two magnitudes. 

The position of the ecliptic in the sky is therefore of great 
importance, and since it is tilted at about 23 Vi degrees to the 
equator, it is only at certain times of the day or year that it is 
displayed to the best advantage. It will be realized that the Sun 
(and therefore the ecliptic) is at its highest in the sky at noon in 
midsummer, and at its lowest at noon in midwinter. Allowing 
for the daily motion of the sky, these times lead to the fact that 
the ecliptic is highest at midnight in winter, at sunset in the 
spring, at noon in summer and at sunrise in the autumn. Hence 
these are the best times to see the planets. Thus, if Venus is an 
evening star, in the western sky after sunset, it will be seen to 
best advantage if this occurs in the spring, when the ecliptic is 
high in the sky and slopes down steeply to the north-west. This 
means that the planet is not only higher in the sky, but will 
remain for a much longer period above the horizon. For 

68 



THE PLANETS AND THE ECLIPTIC 

similar reasons, a morning star will be seen at its best on 
autumn mornings before sunrise, when the ecliptic is high in 
the east. The outer planets, which can come to opposition (i.e. 
opposite the Sun), are best seen when opposition occurs in the 
winter months, when the ecliptic is high in the sky at midnight. 
The seasons are reversed in the Southern Hemisphere, 
spring beginning at the September Equinox, when the Sun 
crosses the Equator on its way south, summer begins at the 
December Solstice, when the Sun is highest in the southern 
sky, and so on. Thus, the times when the ecliptic is highest in 
the sky, and therefore best placed for observing the planets, 
may be summarised as follows: 

Midnight Sunrise Noon Sunset 

Northern lats. December September June March 

Southern lats. June March December September 

In addition to the daily rotation of the celestial sphere from 
east to west, the planets have a motion of their own among the 
stars. The apparent movement is generally direct, i.e. to the 
east, in the direction of increasing longitude, but for a certain 
period (which depends on the distance of the planet) this 
apparent motion is reversed. With the outer planets this 
retrograde motion occurs about the time of opposition. Owing 
to the different inclination of the orbits of these planets, the 
actual effect is to cause the apparent path to form a loop, or 
sometimes an S-shaped curve. The same effect is present in the 
motion of the inferior planets, Mercury and Venus, but it is not 
so obvious, since it always occurs at the time of inferior 
conjunction. 

The inferior planets, Mercury and Venus, move in smaller 
orbits than that of the Earth, and so are always seen near the 
Sun. They are most obvious at the times of greatest angular 
distance from the Sun (greatest elongation), which may reach 
28 degrees for Mercury, or 47 degrees for Venus. They are 
then seen as evening stars in the western sky after sunset (at 
eastern elongations) or as morning stars in the eastern sky 
before sunrise (at western elongations). The succession of 
phenomena, conjunctions and elongations, always follows the 

69 



1978 YEARBOOK OF ASTRONOMY 

same order, but the intervals between them are not equal. 
Thus, if either planet is moving round the far side of its orbit its 
motion will be to the east, in the same direction in which the 
Sun appears to be moving. It therefore takes much longer for 
the planet to overtake the Sun — that is, to come to superior 
conjunction — than it does when moving round to inferior 
conjunction, between Sun and Earth. The intervals given in the 
following table are average values; they remain fairly constant 
in the case of Venus, which travels in an almost circular orbit. 
In the case of Mercury, however, conditions vary widely 
because of the great eccentricity and inclination of the planet's 
orbit. 







Mercury 


Venus 


Inferior conj. 


to Elongation West 


22 days 


72 days 


Elongation West 


to Superior conj. 


36 days 


220 days 


Superior conj. 


to Elongation East 


36 days 


220 days 


Elongation East 


to Inferior conj. 


22 days 


72 days 



The greatest brilliancy of Venus always occurs about 36 days 
before or after inferior conjunction. This will be about a month 
after greatest eastern elongation (as an evening star), or a 
month before greatest western elongation (as a morning star). 
No such rule can be given for Mercury, because its distance 
from the Earth and the Sun can vary over a wide range. 

Mercury is not likely to be seen unless a clear horizon is 
available. It is seldom seen as much as 10 degrees above the 
horizon in the twilight sky in northern latitudes, but this figure 
is often exceeded in the Southern Hemisphere. This favourable 
condition arises because the maximum elongation of 28 
degrees can occur only when the planet is at aphelion (farthest 
from the Sun), and this point lies well south of the Equator. 
Northern observers must be content with smaller elongations, 
which may be as little as 18 degrees at perihelion. In general, it 
may be said that the most favourable times for seeing Mercury 
as an evening star will be in spring, some days before greatest 
eastern elongation; in autumn, it may be seen as a morning star 
some days after greatest western elongation. 

70 



THE PLANETS AND THE ECLIPTIC 

Venus is the brightest of the planets, and may be seen on 
occasions in broad daylight. Like Mercury, it is alternately a 
morning and an evening star, and will be highest in the sky 
when it is a morning star in autumn, or an evening star in 
spring. The phenomena of Venus given in the table above can 
occur only in the months of January, April, June, August and 
November, and it will be realized that they do not all lead to 
favourable apparitions of the planet. In fact, Venus is to be 
seen at its best as an evening star in northern latitudes when 
eastern elongation occurs in June. The planet is then well north 
of the Sun in the preceding spring months, and is a brilliant 
object in the evening sky over a long period. In the Southern 
Hemisphere a November elongation is best. For similar rea- 
sons, Venus gives a prolonged display as a morning star in the 
months following western elongation in November (in north- 
ern latitudes) or in June (in the Southern Hemisphere). 

The superior planets, which travel in orbits larger than that 
of the Earth, differ from Mercury and Venus in that they can be 
seen opposite the Sun in the sky. The superior planets are 
morning stars after conjunction with the Sun, rising earlier 
each day until they come to opposition. They will then be 
nearest to the Earth (and therefore at their brightest), and will 
be on the meridian at midnight, due south in northern lati- 
tudes, but due north in the Southern Hemisphere. After 
opposition they are evening stars, setting earlier each evening 
until they set in the west with the Sun at the next conjunction. 
The change in brightness about the time of opposition is most 
noticeable in the case of Mars, whose distance from the Earth 
can vary considerably and rapidly. The other superior planets 
are at such great distances that there is very little change in 
brightness from one opposition to another. The effect of 
altitude is, however, of some importance, for at a December 
opposition in northern latitudes the planet will be among the 
stars of Taurus or Gemini, and can then be at an altitude of 
more than 60 degrees in southern England. At a summer 
opposition, when the planet is in Sagittarius, it may only rise to 
about 15 degrees above the southern horizon, and so makes a 

71 



1978 YEARBOOK OF ASTRONOMY 

less impressive appearance. In the Southern Hemisphere, the 
reverse conditions apply; a June opposition being the best, 
with the planet in Sagittarius at an altitude which can reach 78 
degrees above the northern horizon. 

Mars, whose orbit is appreciably eccentric, comes nearest to 
the Earth at an opposition at the end of August. It may then be 
brighter even than Jupiter, but rather low in the sky in 
Aquarius for northern observers, though very well placed for 
those in southern latitudes. These favourable oppositions 
occur every fifteen or seventeen years (1924, 1941, 1956, 1971) 
but in the Northern Hemisphere the planet is probably better 
seen at an opposition in the autumn or winter months, when it 
is higher in the sky. Oppositions of Mars occur at an average 
interval of 780 days, and during this time the planet makes a 
complete circuit of the sky. 

Jupiter is always a bright planet, and comes to opposition a 
month later each year, having moved, roughly speaking, from 
one Zodiacal constellation to the next. 

Saturn moves much more slowly than Jupiter, and may 
remain in the same constellation for several years. The bright- 
ness of Saturn depends on the aspect of its rings, as well as on 
the distance from Earth and Sun. The rings are now closing, 
and are inclined towards the Earth and Sun at quite a small 
angle. They will be seen edge-on in 1979. 

Uranus, Neptune, and Pluto are hardly likely to attract the 
attention of observers without adequate instruments, but some 
notes on their present positions in the sky will be found in the 
April, May and June Notes. 



72 



Phases of the Moon 1978 



New Moon 

d h m 

Jan. 9 04 00 

Feb. 7 14 54 

Mar. 9 02 36 

Apr. 7 15 15 

May 7 04 47 

June 5 19 01 

July 5 09 50 

Aug. 4 01 01 

Sept. 2 16 09 

Oct. 2 06 41 

Oct. 31 20 06 

Nov. 30 08 19 

Dec. 29 19 36 



First Quarter 

d h m 

Jan. 16 03 03 

Feb. 14 22 11 

Mar. 16 18 21 

Apr. 15 13 56 

May 15 07 39 

June 13 22 44 

July 13 10 49 

Aug. 11 20 06 

Sept. 10 03 20 

Oct. 9 09 38 

Nov. 7 16 18 

Dec. 7 00 34 

Jan. 5 11 15 



Full Moon 

d h m 

Jan. 24 07 55 

Feb. 23 01 26 

Mar. 24 16 20 

Apr. 23 04 11 

May 22 13 17 

June 20 20 30 

July 20 03 05 

Aug. 18 10 14 

Sept. 16 19 01 

Oct. 16 06 09 

Nov. 14 20 00 

Dec. 14 12 31 

Jan. 13 07 09 



Last Quarter 

d h m 

Jan. 2 12 07 

Jan. 31 23 51 

Mar. 2 08 34 

Mar. 31 15 11 

Apr. 29 21 02 

May 29 03 30 

June 27 11 44 

July 26 22 31 

Aug. 25 12 18 

Sept. 24 05 07 

Oct. 24 00 34 

Nov. 22 21 24 

Dec. 22 17 41 

Jan. 21 11 23 



All times are G.M.T. 
Reproduced, with permission, from data supplied by the Science Research Council. 

73 



The Planets in 1978 



DATE 
January 


6 
21 


Venus 
281° 
301 


Mars 

129° 

123 


Jupiter 
89° 
88 


Saturn 

151° 

150 


Uranus 

226° 

226 


Neptune 

257° 
258 


February 


6 
21 


321 
340 


117 
114 


86 
86 


149 

147 


226 

227 


258 
258 


March 


6 

21 


356 
15 


113 
115 


86 

87 


146 
145 


226 
226 


258 
258 


April 


6 
21 


34 
52 


119 
124 


89 
91 


145 
144 


226 

225 


258 
258 


May 


6 

21 


70 
89 


131 
138 


94 
97 


144 
145 


224 
224 


258 
258 


June 


6 
21 


108 
126 


146 
154 


100 
103 


146 
147 


223 
223 


257 
257 


July 


6 
21 


144 
161 


163 

172 


107 
110 


148 
150 


223 
222 


256 
256 


August 


6 
21 


178 
193 


181 
191 


114 
117 


152 
154 


223 
223 


256 
256 


September 


6 

21 


208 
220 


201 
211 


120 
123 


156 

158 


223 
224 


256 
256 


October 


6 

21 


228 
231 


221 
231 


125 
127 


159 
161 


225 
226 


256 
256 


November 


6 
21 


225 
218 


243 
254 


129 
129 


163 
164 


227 
228 


257 
257 


December 


6 
21 


219 

227 


265 
276 


129 
128 


164 
165 


228 
229 


258 
259 


Conjunction: 


Jan. 22 





July 10 


Aug. 27 


Nov. 9 


Dec. 10 


Opposition: 





Jan. 22 





Feb. 16 


May 5 


June 8 


74 

















THE PLANETS IN 1978 

Mercury moves so quickly among the stars that it is not 
possible to indicate its position on the star charts at a conveni- 
ent interval. The monthly notes must be consulted for the best 
times at which the planet may be seen. 

The positions of the other planets are given in the table on 
the previous page. This gives the apparent longitudes on dates 
which correspond to those of the star charts, and the position 
of the planet may at once be found near the ecliptic at the given 
longitude. 

Examples: 

(1) Where may the planet Mars be found at the end of 
January? 

The table opposite gives the longitude of Mars at this time 
as 120 degrees. In northern latitudes Chart 1 1 R is approp- 
riate, and shows Mars to be rising at about 18 h , to the 
north of east below the Twins, Castor and Pollux. 
Southern observers will use Chart 12R (southern) which 
shows Mars to be rising about 20 h local time. 

(2) What is the bright planet seen by an observer in 
Sydney, N.S. W., to be setting in the north-west at about 
20 b at the end of April? 

Southern Chart 3L applies, and the longitude of the 
planet is seen to be about 90 degrees. The table opposite 
identifies the planet as Jupiter. 

(3) The Monthly Notes for May state that Mars is 
approaching Saturn. Where may these planets be found 
on the night of May 20? 

The table opposite gives the longitude of Saturn as 145 
degrees, while Mars is at 138 degrees. Observers in 
northern latitudes may use Charts 4R or 5R, showing 
Saturn to be a few degrees to the west of Regulus, with 
Mars still farther west. Both planets set about midnight. 
Conditions are more favourable in the Southern Hemis- 
phere, and Chart 5L (southern) shows these planets to be 
setting to the north of west at about 22 h local time. 



75 



Events of 1978 

Eclipses 

In 1 978 there will be four eclipses, two of the Sun and two of the 
Moon. 
24 March — a total eclipse of the Moon, visible in Australia, 
Asia, Africa, and Europe. 
7 April — a partial eclipse of the Sun, visible in South 

America and Southern Africa. 
16 September — a total eclipse of the Moon, visible in 

Australia, Asia, Africa, and Europe. 
2 October — a partial eclipse of the Sun, visible in northern 
Europe, Asia, and the Arctic regions. 

The Planets 

Mercury may best be seen in northern latitudes as an evening 
star at greatest eastern elongation on 24 March, and as a 
morning star at western elongation on 4 September. 

Venus is in superior conjunction on 22 January, and will be 
an evening star for the greater part of the year. It is at 
greatest eastern elongation on 29 August, and is at 
greatest brilliancy on 3 October. After inferior 
conjunction on 7 November it will be a morning star, 
reaching greatest brilliancy on 14 December. 

Mars will be at opposition in Cancer on 22 January. 

Jupiter is an evening star for the first half of the year, and 
after conjunction on 10 July will be a morning star. There 
is no opposition of Jupiter in 1978. 

Saturn is at opposition in Leo on 16 February. 

Uranus will be at opposition in Libra on 5 May. 

Neptune remains in Ophiuchus and will be at opposition on 
8 June. 

Pluto will be at opposition on 5 April in Virgo. 

Vesta will reach magnitude +5.5 at opposition on 5 June, 
but is then low in the sky in Ophiuchus. 

76 



MONTHLY NOTES • JANUARY 



MONTHLY NOTES, 1978 



January 

New Moon: 9 January Full Moon: 24 January 

Earth is at perihelion (nearest to the Sun) on 1 January at a 
distance of 91.4 million miles (147.1 million km). 

Mercury is a morning star, coming to greatest western elonga- 
tion on 1 1 January (23 degrees). It should then be visible above 
the eastern horizon just before sunrise, and is brighter after 
greatest elongation. The planet is well south of the Equator, 
and will be better placed for observers in the Southern Hemis- 
phere. 

Venus is in superior conjunction on 22 January, and will not be 
visible during the month. After conjunction, the planet will 
slowly emerge as an evening star. 

Mars is at opposition on 22 January, reaching magnitude— 1 . 1 . 
The planet will be at its closest to the Earth on the 19th, at a 
distance of 60.7 million miles (97.7 million km). Mars is 
moving retrograde in Cancer, and passes north of the star 
Gamma Cancri and the star cluster Praesepe (M44). This is not 
a particularly favourable opposition, and it may be compared 
with that of 1971, when the distance was only 35 million miles, 
and the magnitude reached —2.6. 

77 



1978 YEARBOOK OF ASTRONOMY 

Jupiter was at opposition in December last, and is still visible 
for most of the night. It will be seen on the borders of Gemini 
and Taurus, moving retrograde to the north of Orion. Magni- 
tude —2.3 to -2.2. (See diagram in November notes.) 

Saturn rises in mid-evening and will be found in Leo to the east 
of Regulus. The planet is moving retrograde, and will pass 
about a degree north of Regulus on 20 January. This is the 
second of three conjunctions with Regulus, caused by the loop 
in Saturn's path. The first was in November last, and the third 
will be in July. Saturn grows brighter during the month as it 
approaches opposition. (Magnitude +0.6 to +0.4.) 



• 








• 

• 


Castor^ 

/ 

Pollux^ 








1 LEO 

-• 


1 Jan ^- ^ -~~ 
_ ^ CANCER 


1 Feb Mar 
- 1 — — ^ 

-r 
Apr 

GEMINI 












Sept 


Fkk,^' June 


• 




Nov, 


\July 




• 
. HYDRA 


CANIS 
MINOR 












Procyon^ 






















• 





Mars and Saturn 1978 



78 



MONTHLY NOTES • FEBRUARY 



February 



New Moon: 7 February Full Moon: 23 February 

Mercury is in superior conjunction on 27th February, and will 
not be seen during the month. 

Venus is now theoretically an evening star, but is too close to 
the Sun to be seen. Venus is well south of the Equator, but is 
moving north, and during the spring months it will be more 
readily observable in northern latitudes. 

Mars is an evening star, still moving retrograde and passing 
into Gemini at the beginning of the month. Mars will be 3 
degrees south of Pollux on 17 February. During the month the 
brightness of the planet diminishes rapidly (magnitude —1.0 to 
-0.3). 



Jupiter reaches a stationary point on 20 February in Taurus, to 
the north of Orion, and after this date it resumes its direct 
motion. The planet sets to the north of west just before dawn in 
northern latitudes, but at midnight for southern observers. 
Magnitude -2.2 to -2.0. 

Saturn is at opposition on 16 February at a distance of 766 
million miles (1,232 million km). It will then be in Leo, about 3 
degrees west of Regulus (see diagram in January notes). The 
rings are tilted at an angle of about 1 1 degrees, and the south 
side is presented to the Earth. The planet reaches magnitude 
+0.3 at opposition, but it can be much brighter than this when 
the rings are open more widely. 

79 



1978 YEARBOOK OF ASTRONOMY 



March 

Summer Time in Great Britain and Northern Ireland com- 
mences on 19 March. 



New Moon: 9 March Full Moon: 24 March 
Equinox: 20 March 

Mercury is at greatest eastern elongation on 24 March and may 
then be seen as an evening star, well placed for observers in the 



10° 




265° 



270° 275° 

AZIMUTH 
Mercury- March, 1978 



280° 



285° 



Northern Hemisphere. The diagram above shows the changes 
in altitude and azimuth (true bearing from the north through 



80 



MONTHLY NOTES MARCH 

east, south and west) of Mercury on successive evenings when 
the Sun is 6 degrees below the horizon in latitude 52 degrees 
north (this is about 35 minutes after sunset). The changes in 
brightness are roughly indicated by the size of the circles, and it 
will be seen that Mercury is brightest before the date of eastern 
elongation. Venus is in the same part of the sky, but is much 
brighter and sets earlier than Mercury. 

Venus now begins to appear as an evening star to observers in 
northern latitudes, setting more than an hour after the Sun at 
the end of March. The planet crosses the equator on its way 
north in mid-March. Magnitude -3.4. 

Mars reaches a stationary point on 2 March in Gemini (see 
diagram in January notes), and then moves direct, passing 4 
degrees south of Pollux again on the 17th. The planet is 
growing rapidly fainter (magnitude -0.3 to +0.5) as its distance 
increases. In northern latitudes Mars will be visible until dawn, 
but in the Southern Hemisphere it sets shortly after midnight. 

Jupiter is an evening star, and in the Northern Hemisphere will 
be seen in the south at sunset, setting an hour or so after 
midnight. In southern latitudes the planet is much lower in the 
northern sky, and sets before midnight. Jupiter is now moving 
direct in Taurus, near the border with Gemini. (Magnitude 
-2.0 to -1.7.) 

Saturn is still visible for most of the night to observers north of 
the Equator, but in southern latitudes it sets in the early 
morning hours. The planet is moving retrograde in Leo, to the 
west of Regulus and it forms a notable group with the Sickle of 
Leo. Saturn is much brighter than Regulus (magnitude +1.3) 
but loses something of its brightness as its distance increases 
(magnitude +0.3 to +0.5). 

A total eclipse of the Moon on 24 March will be visible in 
Australia and New Zealand, and the end of the eclipse will be 
visible in the British Isles. See note on page 100. 

81 



1978 YEARBOOK OF ASTRONOMY 



April 

New Moon: 7 April Full Moon: 23 April 

Mercury is in inferior conjunction on 1 1 April and will not be 
visible during the month. 

Venus is now north of the Equator and will be seen in the 
western sky in northern latitudes for about two hours after 
sunset. In the Southern Hemisphere it begins to appear as an 
evening star, but even at the end of April it sets only about an 
hour after the Sun. Magnitude —3.4. 

Mars is an evening star, and moves direct into Cancer at the 
beginning of the month. At the end of April it passes between 
the two stars Gamma and Delta Cancri, and north of the star 
cluster Praesepe (M44). Northern observers will see the planet 
in the south at sunset, and it will be visible until dawn. In 
southern latitudes, the planet sets at midnight at the beginning 
of the month. Magnitude +0.5 to +1.0. 

Jupiter moves direct into Gemini and may still be seen in the 
evening sky. In the Northern Hemisphere, it sets at midnight, 
but much earlier for southern observers. (Magnitude -1.7 to 
-1.6.) 

Saturn reaches a stationary point on 25 April a few degrees to 
the west of Regulus. After this date the planet will move 
eastwards again, towards Regulus. Saturn will still be visible 
for most of the night in northern latitudes, but sets shortly after 
midnight in the Southern Hemisphere. By the end of April the 
magnitude will have fallen to +0.6. 

82 



MONTHLY NOTES • APRIL 

Pluto is at opposition on 5 April in Virgo, near the northern 
part of that constellation. The magnitude at opposition is only 
+ 14, the distance from the Earth being 2,735 million miles 
(4,400 million km). This is very little more than the opposition 
distance of Neptune (see June notes). 

A partial eclipse of the Sun on 7 April will be visible in parts of 
South Africa (see note on page 100). 



83 



1978 YEARBOOK OF ASTRONOMY 



May 



New Moon: 7 May Full Moon: 22 May 

Mercury is at greatest western elongation on 9 May (26 
degrees) and will then be a morning star. It is too low to be well 
seen in northern latitudes, but is well placed for observers in the 
Southern Hemisphere. At 35 degrees south, Mercury, rises 
about two hours before the Sun on the 10th, and will be seen 
above the eastern horizon. The planet was at aphelion on 30 
April, and is not very bright — magnitude +0.6 on the 12th, but 
brighter after this date. 

Venus is now at its farthest point north of the Equator, and well 
placed for observation in the Northern Hemisphere. At 52 
degrees north it sets to the north of west more than two hours 
after the Sun. Venus will be seen close to Jupiter on the evening 
of 28 May, and the actual conjunction (Venus 1.6 degrees north 
of Jupiter) at 29 May 02h G.M.T., should be worth observing 
in North America. Magnitude —3.4. 

Mars is an evening star and moves into Leo towards the end of 
the month. The planet will be seen to have a rapid direct 
movement towards Saturn, and the changes in position as it 
overhauls the brighter planet will be worth observing. Magni- 
tude of Mars +1.0 to +1.4. In southern latitudes Mars sets 
before midnight, but northern observers have about two hours 
longer to look for the planet. 

Jupiter is now in the western part of Gemini, giving an 
unfamiliar appearance to the well-known group. The planet is 
moving direct, but will be passed by the more rapidly moving 

84 



MONTHLY NOTES • MAY 

Venus on 29 May (see note above). The two bright planets will 
be seen to set together to the north of west about two hours 
after sunset. 

Saturn may be seen in the evening sky until shortly after 
midnight in northern countries, but in the Southern Hemis- 
phere it sets at midnight in early May and well before this by 
the end of the month. The planet is moving slowly eastwards 
towards Regulus, and loses a little more of its brightness 
(magnitude +0.6 to +0.8). 

Uranus is at opposition on 5 May in Libra, very close to the 
third magnitude star Alpha Librae (Zuben-el-Genubi). The 
planet moves very slowly and it should be possible to find it 
close to the star at the end of April and in early May. The 
magnitude at opposition is +5.7 and the distance 1,638 million 
miles (2,636 million km). Uranus should be visible to the naked 
eye at this time, but a small telescope will show it as a greenish 
disk. 

Vesta comes to opposition in June, but it should be possible to 
find this bright minor planet during May, when it is brighter 
than the sixth magnitude. 



.' 



OPHIUCHUS 



June ~ — -- .Julv -»--• 



June"~~---._.July 
/ VESTA 

_• Mar. !S?* Aug -"'' 

^Veptune §e - pt , % 



t i 



• 



/ SCORPIUS 




Uranus, Neptune and Vesta, 1978 

85 



1978 YEARBOOK OF ASTRONOMY 



June 

New Moon: 5 June Full Moon: 20 June 

Solstice: 21 June 

Mercury is in superior conjunction on 14 June and will not be 
visible. 

Venus now begins to move south, and this causes considerable 
changes in the visibility of the planet north and south of the 
Equator. In the north, Venus begins to set earlier each evening, 
but is still well seen in the evening sky, setting to the north of 
west more than two hours after the Sun. In the south, Venus 
sets later each evening, and by the end of the month is visible 
for nearly three hours after sunset. Venus begins to grow 
brighter as its distance decreases (magnitude -3.4 to -3.5). 

Mars is moving direct in Leo, and at midnight on 5 June it 
passes only 0. 1 degrees south of Saturn (see diagram below). At 
this time the motion of Mars is about eight times as great as 
that of Saturn, and the rapid change of position should be quite 
noticeable. Mars passes less than a degree north of Reguluson 
1 2 June. In northern latitudes the planet sets at midnight at the 
beginning of the month, but in the Southern Hemisphere it sets 
in mid-evening. Magnitude +1.4 to +1.6. 

Jupiter is now approaching conjunction and sets shortly after 
sunset. The planet continues to move direct through Gemini, 
and although the magnitude is now only -1 .4, it is still brighter 
than any of the stars in this group. 

Saturn is still in the western part of Leo, and is drawing close to 

86 



MONTHLY NOTES • JUNE 

Regulus. The conjunction of Saturn with Mars on 5 June is 
mentioned above, but the diagram in the January notes is on 
too small a scale to allow this to be shown. The diagram below 
is on ten times the scale, and shows the paths of Mars, Saturn 
and Venus, and the occurrence of the two conjunctions. For 
northern observers Saturn and Mars will set at midnight in 
early June, but about two hours earlier in southern latitudes. 
Saturn is the brighter of the two planets (magnitude +0.8). 













8 July ^ ''June 
9 ^ ^s^'-J^ , - ' 5 June 






LEO 


* ^*~ 


-^<^ C 






-*" „ " 


10 ■*" 


****,■— — 


„-"\" 




""i, July - 


8 . 


1^"" ^_^-"^ ___ 






*34L«onis || ^ ^J^'" ^-C" 


















^cZ^^ -'"^ 












12 July ^ ^><r -<" 






\*^~~*'^ £' ., - " 












^^isjury - * " y 






^"< 




# 27v Ltonis 


,, ' " 14 June 






_ Regutua 







Conjunctions of Saturn with Mars and Venus 

Neptune is at opposition on 8 June at a distance of 2,720 
million miles (4,380 million km). The planet is then actually in 
the constellation Ophiuchus, but is not visible to the naked eye 
(magnitude +7.7). The position of Neptune at this time is 
shown in the diagram in the May notes. 

Vesta is also in Ophiuchus and comes to opposition on 5 June. 
This is a particularly favourable opportunity to look for this 
minor planet, since it is then at perihelion and reaches magni- 
tude +5.5. See diagram and note on page 85 and the note on 
page 107. 

87 



1978 YEARBOOK OF ASTRONOMY 



July 

New Moon: 5 July Full Moon: 20 July 

Earth is at aphelion (farthest from the Sun) on 5 July, when its 
distance will be 94.5 million miles (152.1 million km). 

Mercury is at greatest eastern elongation on 22 July (27 
degrees) and is then an evening star, well placed for southern 
observers, but very low in the sky in northern latitudes. The 
planet is at aphelion on 27 July and is not very bright, but at 35 
degrees south it will best be seen in the first half of the month, 
setting in the west well over an hour after sunset. 

Venus continues to move south and become a more prominent 
object in the evening sky for southern observers. In northern 
countries it sets less than two hours after the Sun. Magnitude 
-3.5 to -3.7. Venus passes very close to Saturn on 10 July, but 
the actual conjunction takes place at 12h G.M.T. and is not 
likely to be seen. The rapid motion of Venus on succeeding 
nights is shown in the diagram in the June notes. 

Mars is an evening star, setting in the late evening, and at the 
end of July it passes into Virgo. Magnitude +1.6 to +1.7. 

Jupiter is in conjunction with the Sun on 10 July and then 
begins to appear as a morning star, rising shortly before 
sunrise. 

Saturn is still visible in the western sky for an hour or two after 
sunset, moving direct in Leo. The conjunction with Venus on 



MONTHLY NOTES • JULY 

10 July is mentioned above, and Saturn will pass about a 
degree north of Regulus on 19 July. (Magnitudes: Saturn +0.9, 
Regulus +1.3) 



89 



1978 YEARBOOK OF ASTRONOMY 



August 

New Moon: 4 August Full Moon: 18 August 

Mercury is in inferior conjunction on 18 August, and will not 
be visible until the last few days of the month, when it begins to 
appear as a morning star. 

Venus is at greatest eastern elongation (46 degrees) on 29 
August, but it is then south of the Equator and not well placed 
for northern observers who will only see the planet in the 
evening sky for about an hour after sunset. In the Southern 
Hemisphere, it can be seen for more than three hours after the 
Sun has set, and will be well displayed in a dark sky. Venus 
passes rather more than a degree south of Mars on 14 August. 
The planet continues to brighten as it draws nearer to the Earth 
(magnitude -3.7 to -4.0). 

Mars is moving south in Virgo, and crosses the Equator in 
early August. The planet is now a difficult object for northern 
observers, setting only about an hour after the Sun, but in 
southern latitudes it continues to be seen until it sets in mid- 
evening. The crescent moon of 8 August passes very close to the 
north of Mars and the planet will be occulted to observers in 
N.E. Australia (see page 101). Mars is in conjunction with Venus 
on 14 August, but there is a very great contrast between the two 
planets, Mars now being only of magnitude +1.8. 

Jupiter is now a morning star, rising to the north of east in 
Gemini, more than two hours before the Sun in northern 
latitudes. In early August it will be seen to the south of the 
Twins, Castor and Pollux, and at the end of the month it passes 

90 



MONTHLY NOTES ■ AUGUST 

into Cancer. Jupiter grows brighter as it moves out from the 
Sun, but it is already the brightest star in the morning sky 
(magnitude -1.5). 

Saturn is in conjunction with the Sun on 27 August, and is not 
visible, but in the Northern Hemisphere, it will quickly move 
out from the Sun to become a morning star. 



91 



1978 YEARBOOK OF ASTRONOMY 



September 

New Moon: 2 September 
Equinox: 23 September 



Full Moon: 16 September 



Mercury is at greatest western elongation on 4 September (18 
degrees) and may be seen in northern latitudes shortly before 
sunrise above the horizon to the north of east. The diagram 
shows the changes in altitude and azimuth of Mercury on 
successive mornings when the Sun is 6 degrees below the 
horizon; this is about 35 minutes before sunrise in September. 
The changes in brightness are roughly indicated by the size of 
the circles. Mercury is at perihelion on 9 September, and is 
quite bright after the date of elongation. Mercury is in superior 
conjunction on 30 September. 



10° 



O 

I- 



Sept.4 



Aug. 30 




70° 



75° 



80° 



85° 



AZIMUTH 
Mercury-September, 1978 



92 



MONTHLY NOTES • SEPTEMBER 

Venus is now a brilliant object in the evening sky in southern 
latitudes (magnitude -4.0 to -4.3), setting more than three 
hours after the Sun. It is not likely to be seen in the Northern 
Hemisphere since it sets shortly after the Sun. 

Mars also sets about an hour after the Sun in northern 
countries, but it is now at its faintest and will be lost in the 
evening twilight. In southern stations, Mars is still visible as an 
evening star until mid-evening. The planet is moving direct in 
Virgo, and passes about 2 degrees north of Spica on 8 Septem- 
ber. 

Jupiter is now a morning star moving direct in Cancer and very 
conspicuous in this barren part of the sky (magnitude -1.5 to 
—1.6). North of the Equator the planet rises about midnight, but 
much later at southern stations. 

Saturn is also a morning star, moving direct in Leo to the south 
and east of Regulus. At northern stations, the planet emerges 
quickly from the Sun's rays, and by the end of September it 
rises more than two hours before the Sun. In the Southern 
Hemisphere, Saturn rises shortly before sunrise, and is hardly 
likely to be seen, since it is now only of the first magnitude. 

A total eclipse of the Moon occurs on 16 September, the early 
stages visible in Australia and New Zealand, the final stages in 
the British Isles. (See note on page 100). 



93 



1978 YEARBOOK OF ASTRONOMY 



October 

Summer Time in Great Britain and Northern Ireland ends on 
22 October. 

New Moon: 2 and 31 October Full Moon: 16 October 

Mercury was in superior conjunction at the end of September, 
and is not likely to be visible until the end of October. 

Venus reaches greatest brilliancy (magnitude -4.3) on 3 
October and will be a splendid object in the western sky in 
southern latitudes. The planet moves rapidly towards inferior 
conjunction, and sets earlier each evening; by the end of 
October it sets about an hour after the Sun. Venus is now at its 
farthest point south of the Equator, and it will not be seen in 
northern latitudes. The planet passes 7 degrees south of Mars 
on 20 October, and it may be possible to see this conjunction 
from Australia and New Zealand, although Mars is now quite 
a faint object. 

Mars is not likely to be seen in northern latitudes, but south of 
the Equator it may still be visible for an hour or two after 
sunset. The planet moves into Libra at the beginning of 
October, and passes half a degree south of Alpha Librae 
(Zuben-el-Genubi) on the 11th. Mars is overtaken again by 
Venus on 20 October — a very noticeable contrast in brightness 
(Mars +1.7, Venus -4.1). 

Jupiter is still a morning star in Cancer, but in northern 
latitudes it will rise before midnight at the end of the month. It 
will then be close to the fourth magnitude star, Delta Cancri. 

94 



MONTHLY NOTES • OCTOBER 

Jupiter is growing a little brighter as it comes round towards 
the Earth (magnitude -1.6 to -1.8). 

Saturn is a morning star in Leo, south of the well-known figure 
of the Lion. In the Northern Hemisphere it rises in the early 
morning hours in a dark sky, but in the south it will be more 
difficult to observe, rising little more than an hour before the 
Sun. Magnitude +1.1. 

A partial eclipse of the Sun will occur on 2 October, but will not 
be generally visible. See note on page 100. 



95 



1978 YEARBOOK OF ASTRONOMY 



November 

Full Moon: 14 November New Moon: 30 November 

Mercury is at greatest eastern elongation on 16 November (23 
degrees), and it may be seen in southern latitudes as an evening 
star after sunset in the south-west. At 35 degrees south on this 
date, the planet sets nearly two hours after the Sun. Mercury is 
brighter before eastern elongation. 

Venus is in inferior conjunction on 7 November, and after this 
date it begins to appear quite rapidly as a morning star in the 
east at sunrise. Conditions are best in the Northern Hemis- 
phere, and here, by the end of November, Venus will rise more 




Pollux V 



TAURUS 



Mjy_ _ A ^_ J Mar 



CANCER \ July , k ., -,- 

JUPITER-,— --*^" " Jun9 /*~* IJa " *" 

—r-~~ Aug ^-» / 

M44* --' Sept \^ / 

-S'-"Oct GEMINI \> / 

I Dec \ / 



• CANIS 

# Minor 

'* * / HYDRA •Pt-oeyon 




Jupiter, 1978 
96 



MONTHLY NOTES NOVEMBER 

than two hours before the Sun. It will then be of magnitude 
-4.2. 

Mars is still an evening star, but sets shortly after sunset. The 
planet moves through Scorpius into Ophiuchus during the 
month. 

Jupiter is in Cancer and reaches a stationary point on 26 
November near the star Delta Cancri, having passed very close 
to the north of this star on 4 November. In northern latitudes 
Jupiter rises in the late evening to the north of east. For 
southern observers the rising is delayed until after midnight. 
(Magnitude -1.8 to -2.0.) 

Saturn is a morning star in the southern part of Leo, rising 
shortly after midnight in the Northern Hemisphere and some- 
what later in the south. The planet is moving more slowly as it 
approaches a stationary point, and its magnitude is still only 
+ 1.1. Saturn is thus a little brighter than Regulus, and should 
be easily recognized in this part of the sky. 



97 



1978 YEARBOOK OF ASTRONOMY 



December 

Full Moon: 14 December New Moon: 29 December 

Solstice: 22 December 

Mercury is in inferior conjunction on 5 December, and comes 
to greatest western elongation (22 degrees) on 24 December. It 
should be possible to catch a glimpse of this elusive planet in 
the south-east before sunrise from any station having a clear 
horizon. Mercury is brightest after western elongation. 

Venus is again at greatest brilliancy on 14 December (magni- 
tude —4.4). Conditions on this occasion are in favour of 
northern observers, and by the end of the year Venus may be 
seen in a dark sky, since it then rises nearly four hours before 
the Sun. In southern latitudes the planet rises about two hours 
before sunrise. 

Mars is now only a few degrees from the Sun and is not likely to 
be seen. The planet is moving rapidly towards conjunction with 
the Sun in January next. 

Jupiter is now moving retrograde in Cancer, and at the 
beginning of the month is to the east of the star Delta Cancri. 
The planet passes to the north of this star in mid-December. 
Jupiter rises in the early evening (but about three hours later in 
southern latitudes) and is growing brighter as it approaches 
opposition in January 1979. (Magnitude -2.0 to -2.1.) 

Saturn remains in the southern part of Leo, and is at a 
stationary point on 25 December. (See diagram in January 
notes.) For northern observers the planet rises in the late 

98 



MONTHLY NOTES • DECEMBER 



evening, but in the Southern Hemisphere it rises at midnight in 
mid-December, and at the end of the year will be in the north at 
sunrise. The rings are now tilted at only 4 degrees, and Saturn 
remains at magnitude + 1.0. The next opposition of Saturn is in 
March 1979. 



99 



Eclipses in 1978 

In 1978 there will be two eclipses of the Sun and two of the 
Moon. 

(1) A total eclipse of the Moon on 24 March, visible 
generally in Australia and New Zealand, and in Asia. The 
final stages will be visible in South Africa and eastern 
Europe. The eclipse begins at 14h 33m G.M.T. and 
becomes total at 15h 37m. Totality ends at 17h 08m, and 
the shadow of the Earth finally passes off the Moon's 
surface at 18h 12m G.M.T. 

(2) A partial eclipse of the Sun on 7 April, visible only in the 
Antarctic andthe extreme south of South America, and 
also in South Africa. At the Cape, the eclipse begins at 
15h 15m G.M.T. and by 16h 09m about 40 per cent of the 
Sun's disk will be covered by the Moon; the Sun sets 
before the end of the eclipse. 

(3) A total eclipse of the Moon on 16 September, the early 
stages visible in Australia and New Zealand, the final 
stages in Africa and the British Isles. The eclipse begins at 
17h 20m G.M.T. and totality begins at 18h24m. The total 
eclipse lasts until 19h 44m, and the eclipse ends at 20h 48m 
G.M.T. 

(4) A partial eclipse of the Sun on 2 October, visible in the 
Arctic and the northern and eastern parts of Europe and 
Asia. 



100 



Occultations in 1978 

In the course of its journey round the sky each month, the 
Moon passes in front of all the stars in its path and the timing of 
these occultations is useful in fixing the position and motion of 
the Moon. The Moon's orbit is tilted at more than 5 degrees to 
the ecliptic, but it is not fixed in space. It twists steadily 
westwards at a rate of about 20 degrees a year, a complete 
revolution taking 18.6 years, during which time all the stars 
that lie within about 6.5 degrees of the ecliptic will be occulted. 
The occultations of any one star continue month after month 
until the Moon's path has twisted away from the star. It will be 
realized that an occultation, like an eclipse of the Sun, is visible 
only in a restricted part of the Earth's surface, and only a few of 
these occultations will be visible at any one place in hours of 
darkness. 

Only four first-magnitude stars are near enough to the 
ecliptic to be occulted by the Moon; these are Regulus, 
Aldebaran, Spica, and Antares. After a lapse of more than 
fifteen years, the star Aldebaran will again be occulted each 
month during 1978. This star is more than 5 degrees south of 
the ecliptic, and it will undergo a long series of occultations 
lasting more than three years. The series begins in Arctic 
regions, coming slowly south and then moving north again, but 
these events are not likely to be seen in western Europe or 
North America until the end of the year. 

The planets, which have a motion of their own, are not 
usually occulted each month in this way. In 1978, there are two 
occultations of Venus and one of Mars, but the general 
conditions for viewing these are unfavourable. 



101 



Comets in 1978 

The appearance of a bright comet is a rare event which can 
never be predicted in advance, because this class of object 
travels round the Sun in an enormous orbit with a period which 
may well be many thousands of years. There are therefore no 
records of the previous appearances of these bodies, and we are 
unable to follow their wanderings through space. 

Comets of short period, on the other hand, return at regular 
intervals, and attract a good deal of attention from astrono- 
mers. Unfortunately they are all faint objects, and are recovered 
and followed by photographic methods using large telescopes. 
Most of these short-period comets travel in orbits of small 
inclination which reach out to the orbit of Jupiter, and it is this 
planet which is mainly responsible for the severe perturbations 
which many of these comets undergo. Unlike the planets, 
comets may be seen in any part of the sky, but since their 
distances from the Earth are similar to those of the planets their 
apparent movements in the sky are also somewhat similar, and 
some of them may be followed for long periods of time. 

The number of comets under observation in any one year is 
much greater than is generally supposed. The following table 
compares the numbers of newly discovered comets, success- 
fully predicted returns of periodic comets and comets being 
followed from previous years: 



New discoveries 
Predicted and recovered 
Still under observation 



102 



1973 


1974 


1975 


1976 


9 


5 


13 


5 


6 


4 


4 


6 


13 


14 


9 


16 



28 23 26 27 



COMETS IN 1978 

In 1978, the following periodic comets are expected to return 
to perihelion: 

Comet Tempel(l) was discovered in 1867, observed again at 
the next two returns and then lost until it was recovered in 
1967, and seen again in 1972. This is a faint comet with a period 
of 5.5 years, and is predicted to return to the Sun in January. 

Comet Arend-Rigaux, discovered in 1950 by two Belgian 
astronomers, has made four appearances and is expected again 
in February. It has a period of 6.8 years, and at perihelion can 
come inside the orbit of Mars. 

Comet Tempel (2) has made fifteen returns, the first being in 
1873. One of the more regular comets, its orbit is now well 
established, and the next perihelion passage will occur in 
February. Period 5.3 years. 

Comet Wolf- Harrington, discovered by Wolf in 1925, was 
not seen again until it was recovered by Harrington in 1951. It 
was then observed at its returns in 1957, 1965 and 1971, and is 
expected again in March. This comet has a period of 6.5 years, 
and the orbit is inclined at an angle of 18 degrees. 

Comet Whipple has been seen at each of its returns to the 
Sun since its discovery in 1 933 . The orbit lies wholly outside the 
orbit of Mars and has a period of 7.4 years. It is expected at 
perihelion in March. 

Comet Tsuchinshan (I) is one of two comets discovered in 
1965 at the Purple Mountain Observatory near Nanking. It has 
a period of 6.7 years and is predicted to return in May. 

Comet Kojima was mentioned in the 1976 Yearbook, but 
subsequent calculations have shown that the comet made a 
close approach to Jupiter in 1973, and as a result the orbit has 
been altered considerably. The latest figures suggest that the 
period has increased from 6.2 to 7.9 years, while the eccentric- 

103 



1978 YEARBOOK OF ASTRONOMY 

ity of the orbit has also increased. Perihelion is now expected in 
May. 

Comet Ashbrook- Jackson was first seen in 1948, and has 
made four appearances. It has a period of 7.4 years and, like 
Comet Whipple, it has an orbit of small eccentricity with its 
perihelion beyond the orbit of Mars. The next return is in 
August. 

Comet Comas Sold, first seen in 1926, has been recovered at 
each of its returns, the last in 1969. This comet has a somewhat 
larger orbit with a period of 8.9 years, and at aphelion it is well 
beyond the orbit of Jupiter. Its next return to the Sun is 
expected in September. 

Comet Schwassmann- Wachmann (I) has a nearly circular 
orbit with a period of sixteen years, which lies entirely between 
the orbits of Jupiter and Saturn. The motion of this comet is 
very much like that of a planet, and it is visible each year. It is 
remarkable for its sudden outbursts of brightness, which seem 
to have some connection with solar activity. Normally of 
magnitude 18, the comet has been known to reach magnitude 
10.7. This occurred in 1959 and again in 1976. Smaller out- 
bursts occur and this phenomenon is also known with other 
comets. 



104 



Meteors in 1978 

Meteors ('shooting stars') may be seen on any clear moonless 
night, but on certain nights of the year their number increases 
noticeably. This occurs when the Earth chances to intersect a 
concentration of meteoric dust moving in an orbit around the 
Sun. If the dust is well spread out in space, the resulting shower 
of meteors may last for several days. The word 'shower' must 
not be misinterpreted — only on very rare occasions have the 
meteors been so numerous as to resemble snowflakes falling. 

If the meteor tracks are marked on a star map and traced 
backwards, a number of them will be found to intersect in a 
point (or a small area of the sky) which marks the radiant of the 
shower. This gives the direction from which the meteors have 
come. 

The following table gives some of the more easily observed 
showers with their radiants; interference by moonlight is 
shown by the letter M. 



Limiting dates 


Shower 


Maximum 


R.A. Dec. 




Jan. 1-6 


Quadrantids 


Jan. 4 


15 h 28 m +50° 




Mar. 14-18 


Corona Australids 


Mar. 16 


16 h 20 m -48° 




April 20-22 


Lyrids 


April 21 


18"08 m +32° 


M 


May 1-8 


Aquarids 


May 5 


22 h 24 m +00° 




June 17-26 


Ophiuchids 


June 20 


17 h 20 m -20° 


M 


Julyl5-Aug. 15 


Delta Aquarids 


July 25 


22" 36™- 17° 




Julyl5-Aug.20 


Pisces Australids 


July 31 


22 h 40 m -30° 




Julyl5-Aug.25 


Capricornids 


Aug. 2 


20 h 36 m -10° 




July27-Aug. 17 


Perseids 


Aug. 12 


3 h 04 m +58° 


M 


Oct. 15-25 


Orionids 


Oct. 20 


6 h 24 m +15° 


M 


Oct.26-Nov. 16 


Taurids 


Nov. 8 


3" 44"'+ 14 




Nov. 15-19 


Leonids 


Nov. 17 


10 h 08 m +22° 


M 


Dec. 9-14 


Geminids 


Dec. 14 


7 h 28 m +32° 


M 


Dec. 17-24 


Ursids 


Dec. 22 


14 h 28"M-76° 





M=moonlight interferes 

105 



Minor Planets in 1978 

Although many thousands of minor planets (asteroids) are 
known to exist, only about 2,000 of these have well-determined 
orbits and are listed in the catalogues. Most of these orbits lie 
entirely between those of Mars and Jupiter. All of these bodies 
are quite small, and even the largest can only be a few hundred 
miles in diameter. Thus, they are necessarily faint objects, and 
although a number of them are within the reach of a small 
telescope few of them ever reach any considerable brightness. 
Of these, the most important are the 'big four', Ceres, Pallas, 
Juno, and Vesta. Vesta can occasionally be seen with the naked 
eye, and this is most likely to occur at a June opposition, when 
Vesta is at perihelion. This will occur again in 1 978, when Vesta 
comes to opposition on 6 June, and is at perihelion at about 
the same time. The planet should be visible to the naked eye 
throughout the months of May, June and July, and in early 
June it reaches magnitude +5.5. Vesta is then in Ophiuchus, 
and has a rapid retrograde motion (see diagram in the May 
notes). 

Ceres, the largest of the minor planets, comes to opposition 
in Sagittarius on 9 July, but does not exceed magnitude +7.1. 
Pallas is at opposition on 4 June, and this planet, whose orbit 
has the large inclination of 35 degrees, will then be well north of 
the ecliptic, and will be in Hercules, at a magnitude of +8.8. 
Juno, at opposition on 24 July, will then be in Aquila, its 
magnitude being only +9.2. 

The latest observations have fully confirmed the small orbit 
found for the minor planet provisionally called 1976 A A (see 
1977 Yearbook). In October 1976 an even smaller orbit was 
found for the minor planet 1976 UA, detected as a fast-moving 
object on plates taken at Mount Palomar. This planet has a 

106 



MINOR PLANETS IN 1978 

period of 0.775 year, and its mean distance from the Sun is only 
0.84 astronomical unit (about 78 million miles). Calculations 
show that it must have passed the Earth at a distance of less 
than a million miles on 20 October. Only one other planet has 
ever come closer to the Earth; this was the planet Hermes, seen 
for a few days in 1937. 



107 



Some Events in 1979 



Eclipses 

In 1979 there will be four eclipses, two of the Sun and two of the 
Moon. 
26 February — a total eclipse of the Sun, visible in N. 

America and as a partial eclipse in western Europe. 
13 March — a partial eclipse of the Moon, visible in Austra- 
lasia, Africa, Europe and America. 
22 August — an annular eclipse of the Sun, visible in Antarc- 
tica. 
6 September — a total eclipse of the Moon, visible in 
America, Australasia and Asia. 

The Planets 

Mercury may best be seen in northern latitudes as an 
evening star about the time of greatest eastern elongation 
on 8 March, and as a morning star at western elongation 
on 19 August. In the Southern Hemisphere the best dates 
are 29 October (evening star) and 21 April (morning star). 

Venus will be a morning star for the first half of the year, and 
will be at greatest elongation on 18 January. Superior 
conjunction occurs on 25 August. 

Mars is in conjunction on 20 January, and there is no 
opposition during the year. 

Jupiter is at opposition on 24 January in Cancer. After 
conjunction on 13 August it will be a morning star. 

Saturn is at opposition on 1 March in Leo. Conjunction on 
10 September. 

Uranus is at opposition on 10 May in Libra. 

Neptune is at opposition on 10 June in Ophiuchus. 

Pluto is at opposition on 8 April in Virgo. 

108 



PART TWO 

Article Section 



Observatory Fitments 

F. R. SPRY 

A keen observer working in his observatory may, in my 
opinion, be described as one of the 'sighted blind'. He has one 
eye to the eyepiece and is viewing in the dark, not daring to put 
on a light which would destroy his night vision for an annoy- 
ingly long time. All he can see is his Moon, planet or star. 

Under these circumstances, 1 suggest that so far as possible 
all accessories should be ready to hand and easily recognised by 
'feel' alone. In my own case, I have what is termed a Crayford 
eyepiece mounting, in which each optic is in its own separate 
tube. Among the eyepieces, I can distinguish my 40 mm by its 
size and the 20 mm by its plain cylindrical shape, while the 
12 mm is small and the tube has a collar at the end; the 6 mm is 
the same size, but has no tube collar. So each eyepiece tells me 
its size by its 'feel', and I do not have the frustration of having to 
use my eyes to identify them. But one must know where they 
are, and this means fitting out your observatory according to a 
pattern which you know by heart. 

I have tried to put together some of the helpful devices that I 
and my friends have worked out, in the hope that they may 
benefit others. 

One of the most useful, in my opinion, was devised by Roger 
Prout. If he wanted to make a study of — for instance — Ursa 
Major, the Great Bear or Plough, he would dictate on to a tape- 
recorder all the information given in a chosen book. He would 
take the tape in to the observatory, and follow the instructions: 
'The first star in the handle is Alkaid'. . . with details of 
magnitude, spectrum and anything else relevant. Alkaid hap- 
pens to be an ordinary star, but the method is particularly 

in 



1978 YEARBOOK OF ASTRONOMY 

valuable with regard to objects such as doubles and variables; 
one can also give taped instructions as to how to locate them. 
Moreover, a tape can be stopped and re-started at will. 

No responsible viewer observes without recording what he 
has seen and done. For this, a clipboard is a 'must'. A thin piece 
of plywood or perspex with a spring clip at the top to hold the 
paper in place is the basic idea. It can be improved by the 
addition of a light from a small battery — preferably a red light, 
which can be controlled by a dimmer resistance from an old 
radio. It is surprising how little light is needed once your eyes 
are used to the dark after, say, half an hour's viewing, and 
almost all observers I know use a red light. Mine is housed in a 
2 oz tobacco tin fixed to the underside of the board. You also 
need a clip for a pencil, tethered with string. Pen torches are to 
be recommended also, since they give only a small amount of 
light where it is most needed — and remember to lay in a stock 
of spare batteries. 

How many eyepieces do you have, and how often do you 
change them when observing? Where are they when not in 
actual use — and how often have you dropped one? Observa- 
tory floors are often concrete, but a carpet on the floor can 
lessen the risks of damage; and eyepieces should be kept in a 
box, since if left on a shelf they can — and do — roll. 

My 8.5 in. reflector is mounted so that when it is pointing to 
the zenith I can reach the eyepiece comfortably, and do not 
need any packing to give extra height; but when I have younger 
and smaller friends with me, extra height is often needed. Often 
it is surprisingly small — an inch or so. I keep a few pieces of 1- 
in. board, fairly wide (say 9 in. at least) for standing on during 
observing. Stools with legs are not to be recommended, 
because it is easy to forget where the legs are. If you slip, it is 
sheer instinct to grab at the telescope, which is not a very firm 
object — and the results can be most unfortunate! 

1 realize that some observatories are bound to be cluttered 
up with equipment, so that there is no room to spare. All I am 
trying to do is to suggest a few possibilities which may suit you. 

If you are interested in occultations, it is useful to have a 
telephone handy for a time-signal. This is recorded on tape, 

112 



OBSERVATORY FITMENTS 

and a commentary can be added, together with a further time- 
check. This is far better than relying on memory alone. Using 
this method, Roger Prout and I once made an interesting 
discovery of a star's fading out during occultation, and what we 
said was recorded for reference later. (The star proved to be a 
very close binary.) 

Some radio sets with short-wave band enable time signals to 
be available at any moment, from certain stations. 

An old alarm clock is useful to remind you of the time to 
watch for something unusual, such as an occultation, and 
another clock can be set to sidereal time. Supplies of masked 
blanks for planetary sketches are useful— kept in a tin or box to 
protect them from the damp. 

A driven telescope involves moving parts, so do not forget to 
keep the movable parts oiled. Then, some records call for the 
exact position of the observatory, and this can be worked on 
from a large-scale ordnance map; mine is 50 degrees 44 minutes 
16.61 seconds north, 00 degrees 47 minutes 12. 18 seconds west. 

Elementary? Of course. But it is surprising how often the 
most elementary precautions and helpful devices are forgotten. 
Perhaps you have never considered one or two of the hints I 
have given here! 



113 



The Earth and the Moon 



R. MADDISON 

Although legend has it that Newton first began to think 
seriously about gravity when he saw or, according to some 
versions, felt an apple fall from a tree, it is much more likely 
that his interest was aroused by looking at the motion of the 
Moon, since it is obviously held in orbit around the Earth by 
some invisible influence. His attempts to explain its motion 
gave us the Law of Universal Gravitation which was later to 
play a major part in the discoveries of both Neptune and Pluto. 

It was not until the latter part of the last century that 
measurements of the behaviour of very large masses over very 
large distances were of sufficient accuracy to show up minor 
deviations from Newton's Law, but such measurements led to 
the development of the theory of relativity rather than the 
downfall of Newtonian theory — the new ideas being a refine- 
ment of Newton's Law that made it applicable to a much wider 
range of properties and circumstances. 

In spite of our present detailed knowledge of gravity and the 
way it works, the motion of the Moon is subject to so many 
outside influences that it seems almost too complicated to 
understand. The study of the Earth-Moon system is a two- 
body problem that is in itself relatively simple to solve. The 
three-body problem takes account of the added influence of the 
Sun and, although it is much more complex, it can be solved. 
The four-body problem involves the perturbations caused by 
Jupiter and is practically insoluble, but the ten-body problem, 
which would be a much more realistic representation of the 
Solar System, is far too difficult even to contemplate. 

Over the last decade, the Apollo astronauts left several sets 

114 



THE EARTH AND THE MOON 

of laser reflectors on the lunar surface, and it became possible 
to detect deviations in the motion of the Moon less than 10 cm 
in amplitude. As a result we now have access to measurements 
of the Moon's motion which reveal changes that seem almost 
impossible to describe, let alone unravel. 

Most students of the Moon, however, are not concerned 
with the fine details of these perturbations although they are 
well aware of the more obvious phenomena such as the 
librations, the captured rotation, the tides, eclipses, and so on. 
The explanations of these phenomena are much more straight- 
forward, and we will look at them in more detail as we review 
the overall properties of the system. 

GENERAL PROPERTIES 

The Earth 



The general properties of the Earth-Moon system are summar- 
ized in Figure 1, but the following explanations may be useful. 



POLE OF 
A ECLIPTIC 




EARTH 



Figure 1. 



115 



1978 YEARBOOK OF ASTRONOMY 

The Earth has a polar diameter of 12,713 km, but because of 
its rapid axial rotation, and the consequent centripetal force, it 
bulges into an oblate spheroid having an equatorial diameter 
of 12,756 km. Detailed surveying using analyses of the motions 
of artificial satellites has shown that there are small deviations 
from this shape that are due to the distribution of continents 
and oceans so that, strictly for accuracy, the only way to 
describe the shape of the earth is to call it a geoid. Even this 
shape is not constant, because of the regular cyclical effects of 
the tides caused by the Sun and the Moon. 

The axis of rotation of the Earth is tilted so that the plane of 
the Equator is at 23 degrees 27 minutes to the plane of the 
ecliptic (i.e. the Earth's orbital plane around the Sun). The 
direction of this axis in space, relative to the stars, is nearly 
constant, so that as the Earth moves around the Sun during a 
year the Poles are presented to it at varying angles and we have 
the effects of changing seasons. During summer, for example, 
the North Pole is tilted towards the Sun, whereas six months 
later it is tilted away from it. Careful observations over a long 
period of time will show that this axial direction is not exactly 
constant, but is slowly changing. At present, the Pole Star is 
about 1 degree from the true pole of the Earth's rotation, but 
during the next 12,000 years the true pole will move in an arc 
towards the star Vega. This effect, called precession, is caused 
by the gravitational force of the Sun acting on the tilted bulges 
of the Earth; the full cycle of complete rotation covers a period 
of 25,780 years. 

The mass of the Earth is estimated to be 5.977 x 10 24 kg, and 
if this figure is compared with the volume of the Earth we find 
an average density of 5.52 gm/cc. Geologists estimate that the 
average density of the surface rocks on Earth lies somewhere 
between 2.0 and 3.5 gm/cc and so it is clear that the deep 
underlying rocks must have much higher densities, and that 
there is probably a core of highly compressed material of 
density greater than 10 gm/cc. 

The Moon 

The Moon has a diameter of 3,476 km and has an almost 

116 



THE EARTH AND THE MOON 

perfectly circular profile. Careful measurements have shown 
small deviations from circularity towards an elliptical cross- 
section. These amount to about 2 km, but the true shape is very 
difficult to assess because of the mountains and valleys that 
make up the lunar limb. It is clear that there is no pronounced 
equatorial bulge like the Earth's, but this would not be 
expected for such a slow axial rotation (27.32 days). 

Analysis of the motions of several artificial moon satellites 
has, however, revealed irregular distributions of dense rocks 
immediately beneath some of the prominent maria: the mas- 
cons. This has shown that there is an earthward pointing bulge 
near the centre of the visible disk of about 3 km in height. 

The orbit of the Moon around the Earth is approximately 
elliptical, and varies in distance between 363,263 km at perigee 
and 405,547 km at apogee. This varying perspective is apparent 
on Earth as a variation in the angular size of the Moon between 
32'.9 and 29'.5, and this has important effects on solar eclipses. 

The equatorial plane of the Moon is inclined to its orbital 
plane by 6 degrees 41 minutes, and this orbital plane is inclined 
to the ecliptic by 5 degrees 9 minutes. These inclinations lead to 
a precessional effect similar to the Earth's, but in this case the 
rotation is much more rapid, having a period of only 18.6 
years. 

The mass of the Moon is measured to be 7.35 x 10 22 kg, 
which is a fraction 1/81.3 of the Earth's mass. This implies an 
average density of 3.34 g/cc, which is surprisingly low, and 
indicates, when compared with the surface density, much less 
concentration into a core than for the Earth. 

Orbits 

The orbital motions of bodies in a system are related to the 
gravitational centre of the system. In the Earth-Moon system 
the barycentre lies within the Earth at a point some 1707 km 
beneath the surface. This means that as the Moon rotates 
around the barycentre once a month so also does the Earth in 
an orbit of radius 4,671 km. In addition, both bodies are 
strongly affected by the Sun and, for example, the Moon 
experiences extra gravitational force accelerating its motion 

117 



1978 YEARBOOK OF ASTRONOMY 

while it is moving towards the Sun. On the other side of its orbit 
it moves away from the Sun, and the extra force slows it down. 
On the whole, the Moon follows the general laws of plane- 
tary motion around a centre, and so it moves faster in its orbit 
at perigee, when it is closest to the Earth, and slower at apogee, 
when it is furthest away. 

The Librations 

At any instant of time an observer on Earth can see rather less 

than 50 per cent of the surface of the Moon. This is simply 

because the limb that he sees from a single point is defined by 

tangential rays of light radiating towards his eye. The closer he 

is to the Moon, the smaller is the area of its surface that he can 

see. 

If he watches the Moon for several weeks he notices that the 
limb is not always in the same place. Sometimes he sees 
features in one area that were beyond the limb a few days 
earlier, while at the same time features that were clearly visible 
on the opposite limb are lost to sight over the horizon. He 
notices that the Moon appears to sway and nod as it moves 
along its monthly track around the sky. Careful mapping over 
a number of years shows that he can accumulate observations 
of up to 59 per cent of the total lunar surface. The remaining 
41 per cent is, of course, hidden from view on the far side of the 
Moon. 

This phenomenon is known as the lunar libration, and there 
are three main causes. First, there is the libration in latitude, 
which accounts for the nodding motion. The plane of the 
Moon's equator is inclined at 6 degrees 41 minutes to the plane 
of its orbit, so that sometimes the Moon's north pole is tilted 
towards the Earth by this amount. At such times an observer 
on Earth sees slightly beyond the north pole, while the south 
pole is out of sight. Approximately half an orbit later, due to 
the nearly constant direction of the rotational axis relative to 
the stars, it is the southern pole that appears tilted earthwards 
and the north pole that is out of sight (see Figure 2). 
The second effect is the libration in longitude. In this case, the 
apparent swaying of the Moon is due to a mismatch of the 

118 



THE EARTH AND THE MOON 




Figure 2. 

constant rate of axial rotation and the varying orbital speed. 
Figure 3 is a plan view of the Moon's orbit; it shows the Earth 
at one focus and the successive positions of the Moon at 
quarter-month intervals. It should be remembered that the 
Moon's axial rotation is very constant, like a giant flywheel, 
and that it rotates through a quarter of a revolution in a quarter 



|month 

4 



I MONTH 




MONTH 



fMONTH 
4 



Figure 3. 



119 



1978 YEARBOOK OF ASTRONOMY 

of a month. The orbital speed, on the other hand, is described 
by Kepler's Second Law of planetary motion, so that the Moon 
covers more of its orbit near perigee than it does near apogee in 
the same time interval. The resulting apparent sway to east and 
west, of 6 degrees 17 minutes, allows an observer to see 
alternately beyond the mean eastern limb and then beyond the 
mean western limb. 

The third cause is a purely local one involving the rotation of 
the Earth. In half a day an observer is carried around half ofthe 
Earth's circumference. He may be able to observe the Moon at 
sunset over in the east and then to follow it across the sky until 
it is in the west at dawn. During this time his view ofthe moon 
has changed because he sees it from different positions along a 
baseline of more than 12,000 km. This effect, small compared 
with the others, is called the diurnal effect. 

The Tides 

Since the Earth and the Moon are plastic bodies that can be 
deformed by large forces, for example by rapid axial rotation, 
then it is not surprising that one can observe the mutual effects 
of gravity on the shapes of the two bodies. This is the pheno- 
menon of tidal deformation, and is observable in the solid 
masses of the Earth and Moon as well as in the oceans and 
atmosphere of the Earth. The situation is complicated by the 
presence of the Sun, with the result that the tide-raising forces 




EARTH \ M00N 

Figure 4. 



120 



THE EARTH AND THE MOON 

are sometimes high, due to both bodies acting together and 
giving rise to 'spring' or very high tides. At other times the Sun 
and Moon act in opposition and give 'neap' or relatively low 
tides. 

Most people are familiar with the fact that two tidal bulges 
occur on Earth, one on the moonward side and the other on the 
opposite side (points A and C in Figure 4) but many find it 
difficult to see why there should be a bulge on the side of the 
earth away from the tide-raising force. This is a difficulty that 
arises because we are used to feeling gravity acting downwards 
towards the centre of the Earth and we have an in-built frame 
of reference that regards the centre of the Earth as the origin in 
the system. The real situation becomes clear if we move our 
frame of reference to the point A on the far side of the Earth. 
We know that the force of gravity obeys an inverse square law, 
and we can see that the point A experiences a certain gravita- 
tional force due to the Moon. At the centre of the Earth, point 
B, we are much nearer to the Moon than at A and there is 
consequently a much stronger gravitational attraction. This 
causes a differential force between A and B that has the effect 
of pulling the centre of the Earth away from the edge at point 
A. As a result the seas are left behind and build up into a bulge. 
The same situation applies to the moonward side, so that there 
is a stronger attraction at point C than at the centre and this 
pulls the seas off the Earth into another bulge. 

The existence of these two separate bulges causes two high 
tides each day at any point on the surface. Effectively the Earth 
rotates underneath the bulges. Figure 4 shows how a typical 
point (F) on the Earth's surface experiences these daily tides 
and how they are generally of different heights. 

The actual tidal motion of the seas is quite small, but it is 
complicated and magnified by the presence of various surface 
features such as the continental masses. In some shelf areas 
like, for example, the Bay of Fundy in North America, the 
difference between high and low tide can be as much as 16 
metres. In central ocean areas like the island of Tahiti, where 
there is much less disruption of free flow, the tidal range is as 
little as half a metre. 

121 



1978 YEARBOOK OF ASTRONOMY 

Tides also affect the solid body of the Earth, and the rocks 
distort to the extent of about a metre. The interesting fact is 
that this distortion relaxes as soon as the force is reduced so 
that it seems as if the planet behaves like a perfectly elastic 
sphere. 

Tidal forces between two bodies are, of course, mutual and 
there is a matching distortion of the solid body of the Moon. It 
is estimated that the bulge in the centre of the visible face of the 
Moon is about 95 metres high but it is still not possible because 
of observational difficulties, to say that there is a bulge on the 
hidden side. Although these figures are so small the distortions 
have had several interesting cumulative effects on the Moon 
over the aeons of time that have elapsed since the system was 
formed. 

Captured Rotation 

When the Earth -Moon system originated some four and a half 
thousand million years ago, it is fairly certain that the process 
involved was the gravitational capture of the Moon by the 
Earth, and that the bodies were never linked together as some 
of the early theories supposed. If this was the case, then it is 
most unlikely that the period of axial rotation of the Moon 
would be equal to its orbital period. The present situation is 
one that must have developed over a long period of time due to 
tidal interactions, and the chances are that the Moon's axial 
period was once much shorter than it is now. 

The present captured rotation, where we always see the same 
face from Earth, is easy to explain if we remember that there is 
a tidal bulge near the middle of the Moon's visible face. The 
tide-raising force is primarily due to the Earth, and one would 
expect the bulge to be formed in the direction of this force. In 
the early days, however, the Moon would be rotating in a non- 
synchronous fashion, which would mean that the bulge would 
have to move over the lunar surface in order to stay in the same 
direction relative to the Earth. There would be a continuous 
plastic deformation of the Moon as it rotated underneath the 
bulge. This process would obviously involve considerable loss 
of energy because of the viscous drag of the bending rocks, and 

122 



THE EARTH AND THE MOON 

it would become progressively harder to move the bulge as the 
Moon cooled down and became more rigid. 

Over a long period of time this effect, which is like applying a 
steady braking force to a heavy flywheel, would slow the 
rotation down until the minimum amount of energy is lost in 
the process, and this would correspond to synchronous rota- 
tion where the bulge does not need to wander about over the 
surface. The same situation would have prevailed if the original 
period of axial rotation had been much longer than a month, 
but in this case the frictional drag would have slowly increased 
the rate of axial rotation. 

In either case there would be a compensating effect on the 
Earth so that angular momentum is conserved, but there would 
be an overall loss of energy in the slight heating due to viscous 
drag. 

The Recession of the Moon 

Another interesting side effect of the tidal deformation of the 
earth is that its produces a gradual increase in the Moon's 
orbital speed which, in turn, makes the Moon slowly recede. 

ORBIT OF 
\ MOON 




123 



1978 YEARBOOK OF ASTRONOMY 

Figure 5 is a plan view of the Moon's orbit. It represents an 
instantaneous view of what is, in reality, a state of dynamic 
equilibrium. The Earth-Moon gravitational interaction gener- 
ates the two bulges in the viscous but plastic body of the Earth, 
but the Earth has an axial rotation which is very much faster 
than the orbital rotation of the Moon. The effect of the 
frictional drag is that the bulges are carried around by the 
Earth's rotation until a balance is set up between the drag and 
the tide-generating force. 

On Earth, an observer has the impression that the tides occur 
before the Moon crosses his meridian, almost as if the tidal 
bulges are anticipating the presence of the Moon. 

One way of representing this situation in terms of forces is to 
regard the Earth as a double object having two gravitational 
centres, for example, at the foci of the ellipse produced in a 
cross-sectional view. At equilibrium point A (Figure 5) is 
nearer to the Moon than point B and is therefore experiencing 
a stronger gravitational attraction than B. Both A and B are 
displaced from the central line so that the forces along AC and 
BC converge towards the centre of the Moon. These two forces 
may be resolved at the Moon into components that act in one 
case along the central line towards the Earth, and in the other 
case at right angles into the direction of the Moon's orbit. The 
components acting towards the centre add together, whereas 
the components in the direction of the orbit are in opposition. 
Because the force along AC is larger than that along BC, there 
remains a net unbalanced force acting on the Moon in the 
orbital direction which has the effect of accelerating its motion. 
It thus moves into an orbit of larger radius and modern 
estimates indicate a recessional speed of about 3.2 cm per year. 

This effect is, of course, accompanied by a slowing of the 
Earth's axial rotation — since angular momentum has to be 
preserved — and there is indeed strong geological evidence that 
the days were shorter in the remote past than they are now, and 
there were more of them in a year. 

The Roche Limit 

The Moon's very slow recession can be used to suggest that 

124 



THE EARTH AND THE MOON 




Figure 6. 

perhaps, in the remote past, the Moon and the Earth were very 
close together and may in fact have been joined as a single 
object. There are, however, good dynamical reasons why such 
an object would be very stable, and it is difficult to see how it 
could break up even if it were only loosely held together and 
still contracting under gravity. There is also a good reason why 
something as large as the Moon would be unable to exist as a 
single object very close to the Earth, even if it had successfully 
been able to break away from it. The argument is as follows: 
the nearside of the Moon (at A in Figure 6) experiences a 
gravitational force F„ due to the Earth. The far side experi- 
ences a much smaller force F 2 , since it is 3,476 km further 
away. There is, therefore a differential force, F,~ F 2 , acting 
across the Moon which is literally trying to pull it apart. Since 
both F, and F 2 are determined by an inverse square law of 
distance, it is possible to find a point at a critical distance from 
Earth at which this differential force becomes equal to the 
cohesive force that holds the Moon together. This cohesive 
force is the gravitational attraction that formed the Moon 
originally, and it is also the gravitational attraction any object 
would feel at its surface. 



125 



1978 YEARBOOK OF ASTRONOMY 

At a point closer to the Earth than this distance, the Moon 
would be torn apart by the differential force and the fragments 
would probably spread around the Earth and form a ring 
system exactly like the one around Saturn. 

The particular critical distance for any planet is known as the 
Roche Limit, and it depends both on the relative dimensions of 
the bodies involved and their masses. In the case of the 
Earth-Moon system the Roche Limit is about 16,000 km, 
which is a point roughly 10,000 km above the surface of the 
Earth. 



Eclipses and the Saros 

One of the most helpful and fortuitous arrangements in 
astronomy is the near equality of the apparent angular sizes of 
the Moon and Sun as seen from Earth. On occasions the 
Moon's disk can exactly mask the brilliant solar photosphere 
so that we can see the corona, the chromosphere and promi- 
nences without specially designed equipment. 

The varying distances of the Moon from Earth and the Earth 
from the Sun combine to give us a range of possible eclipses as 
the relative sizes of the Moon and Sun change. If an eclipse 
takes place when the Earth is at perihelion and the Moon at 
apogee, the Sun appears 1' 35" larger than the Moon and the 
Sun is not completely obscured. Under these circumstances the 
Moon's shadow does not reach the Earth (case B in Figure 7), 




RAYS FROM 
SUN 



Figure 7. 



126 



THE EARTH AND THE MOON 

and a bright ring of the Sun is visible around the Moon. This 
'annular' appearance can last for a maximum of 12 min 24 sec. 
Conversely, when the Earth is at aphelion and the Moon at 
perigee (case A Figure 7.), an eclipse can occur where the Moon 
is 1 '19" larger than the sun and totality can last for as long as 
7 min 40 sec. The great African solar eclipse of 1973 (June 30) 
was close to this situation, the greatest duration at that time 
was 7 min 5 sec. 

In order to see a total eclipse one has to be at some point on 
the track of totality as the Moon's shadow moves across the 
Earth. Such tracks are at most about 250 km wide and it is 
therefore not surprising that many of the Earth's inhabitants 
have never seen one. 

On the other hand, a total lunar eclipse, where the Moon 
passes into the much bigger shadow of the Earth (case C, 
Figure 7), is visible to anyone in the appropriate hemisphere of 
the Earth. The size of the Earth's shadow is such that a total 
eclipse of the Moon can last for up to 104 minutes. Because of 
this, there is a distinct impression that lunar eclipses must be 
more common than solar eclipses. In fact, the opposite is true. 
Figure 7 shows how the area of sky on the sunward side of 
Earth, in which a solar eclipse might take place, is considerably 
larger than the area covered by the Earth's shadow at night. 
This means that over a long period of time there are more solar 
eclipses than lunar eclipses. 

Because the plane of the Moon's orbit and the plane of the 
ecliptic are not the same, eclipses do not occur every month. 
Figure 8 shows the orientation of these two planes just before a 
solar eclipse. One of the nodes, or points of intersection of the 
two planes, must be in the direction of the Sun, so that as the 
Moon approaches the node it must also pass in front of the 
Sun. If these conditions can be satisfied it can be shown that 
there may be between two and five solar eclipses in a year. 

The prediction of eclipses is an art that was known to the 
ancient Babylonians, and it depended on a careful knowledge 
of the relative motions of the Sun and Moon and involved 
knowledge of the cycle of eclipses known as the Saros. 

Solar eclipses, by definition, occur at new moon, so the time 

127 



1978 YEARBOOK OF ASTRONOMY 



7*- 



/ 




MOON OR*"* / 

' LINE OF NODES 

Figure 8. 

interval between successive new moons, the synodic month, is 
clearly an important factor. It was noticed by the early 
observers that during an interval of 223 synodic months the 
Sun makes a complete circuit of the sky and reaches the same 
node at the same place on the ecliptic. This length of time is 
6585.321 solar days, which is 18 yrs and 11 '/-, days. 

The shortest time required for the Sun to travel from and 
return to the same node is 346.6 solar days, and this interval is 
known as an eclipse year. It is less than a calendar year because 
of the effect of orbital precession, mentioned earlier, that 
causes a slow regression of the nodes around the ecliptic. 
Nineteen of these eclipse years contain 6585.4 days, which is 
almost precisely 223 synodic months. The coincidence of these 
two periods means that, if an eclipse occurs at a node at a 
certain point on the ecliptic, it will be repeated in almost the 
same point after 18 yrs liy 3 days. This period of time is the 
Saros. In effect, a cycle of eclipses repeats with this periodicity 
and, although the tracks of totality will not coincide on the 
Earth's surface, the appearances of the eclipses will be the 
same. 

128 



THE EARTH AND THE MOON 

If one takes account of the slight mismatch of 223 synodic 
months and nineteen eclipse years, and calculates the exact 
period of the complete cycle then the result is a series of eclipses 
lasting for about 1,200 years. 

This brief summary of the more obvious properties of the 
Earth-Moon system shows how complex the interactions are. 
When we bear in mind that the Moon is our closest neighbour, 
and yet we do not fully understand its behaviour, we may 
realize how little we know of the rest of the Universe. This is 
probably why astronomy is such a fascinating pursuit! 



129 



The Zodiacal Light 



J. C. D. MARSH 



The constellations of the Zodiac are probably the most familiar 
(in name) after the Plough or Great Bear. There are twelve of 
them, each occupying about 30 degrees of the sky, although 
their shapes are by no means regular. They are threaded by that 
imaginary path called the ecliptic along which the Sun appar- 
ently moves throughout the year, passing through one constel- 
lation each month. Indeed, the Moon and the principal planets 
never stray more than a few degrees north or south of the 
ecliptic, so that the region of sky through which these objects 
pass is made up of a strip containing the Zodiacal constella- 
tions. 

VERNAL 

EQUINOX 

- MAR 22 



WINTER 
SOLSTICE 



SUMMER 
SOLSTICE 




AUTUMNAL 
EQUINOX 

Figure I. The Zodiacal constellations, ecliptic and equator 



130 



THE ZODIACAL LIGHT 

There is, however, another phenomenon of great delicacy 
apparently associated with the ecliptic which may be seen on a 
moonless night, when the atmosphere is at its clearest and most 
transparent. This is the Zodiacal Light. 

About an hour after sunset, above where the Sun has 
dropped below the horizon, a faint diffuse area of light may be 
seen shaped rather like a slanting cone with its axis curving 
slightly back up along the ecliptic. At its base, it is perhaps 15- 
20 degrees wide and it extends upwards for rather more than 20 
degrees. On long-exposure photographs, it can be seen to 
extend up to twice this distance. 



ECLIPTIC 




WESTERN HORIZON 

Figure 2. The Zodiacal Light after sunset 



At its brightest, towards the centre of the cone, it is several 
times more luminous than the band of the Milky Way, and the 
distribution of light is more even than the familiar stippled 
effect of the Milky Way. 

It is not too well seen from temperate latitudes, probably due 
to the angle which the ecliptic makes with the horizon and the 
long duration of twilight. In tropical regions, however, the axis 
of the cone is more nearly vertical and the twilight lasts only for 
a short time, so that from these zones the Zodiacal Light is 
more readily apparent. At greater angular elongations from 
the Sun, the Zodiacal Light may be seen to extend right across 
the sky from western horizon to eastern horizon to form a faint 

131 



1978 YEARBOOK OF ASTRONOMY 

but discernible zodiacal band, with a small bulge at the anti- 
solar point called the Gegenschein. However, from eclipse 
observations the Zodiacal Light can be seen to extend towards 
the limb of the Sun, where it merges with the solar corona. 
It appears to have been first observed by Cassini, around 
1683, who suggested even then that it was associated with 
reflected sunlight. However, it is such a delicate phenomenon 
that the definitive measurements necessary to ascertain its 
brightness, colour, spectrum and polarization were not possi- 
ble until a comparatively few years ago. And it is these 
measurements which have now allowed this delicate and 
beautiful phenomenon to be fairly well understood. 

The Colour and Spectrum 

Roach and Jammick (1958) have correctly pointed out that the 
brightest portions of the Zodiacal Light are about 100 times 
too faint for colour perception to be possible with the normal 
human eye. 

However, 12-colour photometry, i.e. measurements of the 
intensity of the light at precisely defined wavelengths and 
bandwidths, was undertaken over a long period in the grounds 
of the McDonald Observatory, Texas (elevation 6,800 ft) by 
Alan W. Peterson which yielded a colour index B-V = 0.6 1± 
0.02 which compares almost exactly with that of the Sun, B-V 
= 0.62 (Allen, 1963). This gives a substantial reason for 
anticipating that what we see is reflected sunlight. Moreover, 
high-resolution spectroscopy of the Zodiacal Light carried out 
by Blackwell and Ingham (1961) revealed many individual 
absorption lines which are directly identifiable with the lines 
of solar spectrum. So it appears that sunlight plays a predomi- 
nant part in generating the Zodiacal Light. 

How does it do this? 

The Composition of the Zodiacal Light 
Polarization measurements suggest the presence of many small 
dust particles forming a zodiacal cloud. Exploratory calcula- 
tions show that as well as larger particles the presence of 
particles with radii in the region in the range 0. 1 to 0.2 microns 

132 



THE ZODIACAL LIGHT 

(a micron is one millionth of a metre) should not be excluded. 
Early theories suggested that particles with radii less than 0. 1 to 
0.8 microns would be blown out of the Solar System by the 
Sun's photon and corpuscular radiation, but there are several 
mechanisms which modify the effects of radiation pressure. 
Also there are several sources which give a continual supply of 
submicron particles. Another objection to submicron inter- 
planetary particles is based on the argument that such particles 
are incompatible with the observed colour of the solar F 
Corona. However, there is no reason to assume that the size 
distribution of dust close to the Sun is the same as for the 
Zodiacal Light. In fact, large particles are continually being 
pulled into a smaller and smaller volume around the sun by 
Poynting-Robertson forces — submicron particles are not. 
Powell et al. (1967) proposed a belt model of interplanetary 
dust. In this, the interplanetary space in the plane of the ecliptic 
is arbitrarily separated into a system of belts such that the 
boundary of each belt coincides with the orbits of the planets. 
It is further assumed that all particle sizes and refractive indices 
are possible and that size distribution, number density and 
chemical composition of particles in one belt are completely 
independent of the same quantities in another. Finally, it is 
assumed that the particles are spherical. 

Analysis of observations of the Zodiacal Light allow the size 
distribution of particles in each belt to be ascertained. These 
indicate that the radii of the particles lie in the range 0.08 to 1 .5 
microns, and the decrease in the number density with increa- 
sing particle size is very steep. Details are beyond the scope of 
this article, but the conclusions are clear; the dust particles near 
the Earth's orbit have radii between 0.08 and 0.2 microns and a 
dialectric constant lying between 1.4 and 1.8. There is little 
reason to expect the axis of the Zodiacal Light to coincide 
exactly with the ecliptic, for the ecliptic is defined by the orbital 
plane of the Earth, an insignificant planet. If the light is 
reflected by small solid particles, gravitational forces might be 
expected to be the dominant ones and a more significant plane 
would be the invariable plane of the Solar System which is 
inclined 1 degree 39 minutes to the plane of the ecliptic. Such a 

133 



1978 YEARBOOK OF ASTRONOMY 

small displacement is difficult to detect, even with delicate 
measurements, and for visual observations, quite impossible. 

Thus, we may be fairly confident that the Zodiacal Light is 
due almost entirely to the scattering of sunlight by minute dust 
particles in the interplanetary space surrounding Earth, possi- 
bly concentrated by gravitational forces into a thicker belt 
coincident with the invariable plane of the Solar System. 

As an observational phenomenon it is well worth looking 
for, preferably from a high site under clear dark conditions, 
whilst from a scientific point of view a study of the Zodiacal 
Light has yielded valuable information on the composition, 
density, size and distribution of dust particles in interplanetary 
space. Finally, a review article entitled 'The Zodiacal Light' by 
Blackwell, Dewhirst and Ingham in Advances in Astronomy 
and Astrophysics 1967 offers a great deal of further informa- 
tion than this short article. 



References 

Roach, F. E., and Jammick, P. Sky and Telescope, 17, 164, 1958. 

Peterson, A. W. NASA Symposium, SP-150, 1967. 

Allen, C. W. Astrophysical Quantities, Athlone Press, 1963. 

Blackwell, D. E., and Ingham, M. F. MNRAS, 122, 113, 1961. 

Powell, R. S., et al, NASA Symposium, SP-150, 1967. 



134 



Craters on Mercury and Mars 



S. MIYAMOTO 

Craters are characteristic landforms on the Moon, covering its 
whole surface. In 1965, Mariner 4 detected craters on Mars 
also, and more detailed studies of them have been carried out 
from Mariners 6 and 7 (1969), Mariner 9 (1971) and Vikings 1 
and 2 (1976). And in 1974, Mariner 10 discovered that Mer- 
cury, also, is cratered, so that it may be that craters are 
characteristic of terrestrial-type planets. However, the craters 
in each of these worlds show their own individuality in their 
morphological features. 

The observed hemisphere of Mercury shows craters which 
look very like those on the Moon, and ray-craters also exist. 
Many of the Mercurian craters have central peaks, some of 
which have well-developed outer slopes and cover large areas 
of the inner floor. In some cases the peaks exhibit summit 
vents. 

On Mars, craters are less abundant than with Mercury or the 
Moon, and their distribution is more restricted. Some are of 
'lunar' type, but there are others which may be termed volcanic 
domes, snowing a large summit vent rather than a crater. There 
are also various other features on Mars, such as large grabens, 
valleys, and strato-volcanoes. 

We are now able to arrange craters in definite classes. At the 
end of the sequence come craters such as Ptolemaeus and 
Clavius, on the Moon — large, with polygonal walls and rather 
flat floors. The surrounding areas are covered with tectonic 
networks, and the crater walls are associated with these 
network features. 

At the other end of the sequence come the strato-volcanoes, 

135 



197K YEARBOOK OF ASTRONOMY 




Figure I . PtolemEus, Alphonsus.Arzachel 



such as Olympus Mons, Arsia Mons, Pavonis Mons, and 
Ascraeus Mons in the Tharsis region of Mars. Between these 
extreme forms comes Tharsis Tholus, east of Ascraeus Mons. 
Its outer wall is too well developed for it to be regarded as a true 
crater, but its summit vent is much larger than for any 
terrestrial volcano. The diameter of the feature is 170 km, and 
there are other similar structures in the same area. Arsia Mons 
may be included in the same group. Morphologically, it may be 
classed as a giant depression, but the height of the crater wall 
above the floor is about 27 km, and the crater itself is 100 km in 
diameter. Its outer slope is not symmetrical, but is about three 

136 



CRATERS ON MERCURY AND MARS 




Figure 2. Olympus Moris 



times greater than the diameter of the crater. Arsia Mons and 
Tharsis Tholus seem to be intermediate morphologically 
between calderas and scoria cones. 

Interesting types of craters were revealed in the Chryse 
region of Mars by the Viking photographs. Arandas (15 
degrees west, 43 degrees north) is 25 km in diameter, and is 
surrounded by a lava-flow; the central peak is very well 
developed, and covers much of the floor. Another crater in the 
Chryse region, Yuty— 18 km in diameter- shows a lobate 
pattern of lava flow; the central peak is a gigantic cone, 
crowned with summit craters. Many other craters in Chryse are 
similar in form. 

As is well known, craters with lobate lava flows are rare on 
the Moon, and on Mercury they are rare and inconspicuous. 

137 



1978 YEARBOOK OF ASTRONOMY 




Figure J. Tharsis Tholus 

Craters of this kind may be placed in our crater sequence 
between formations of lunar type and those of the Arsia Mons 

type. 

Double-ring craters are common on Mercury; Renoir, Bach 
and Bernini are good examples. They have, in fact, central 
calderas instead of central peaks. 

In the Cydonia region of Mars there is a 40-km crater which 
is unlike Arandas or Yuty in that the outer region, beyond the 
wall, is a flat plane pitted with craterlets; the floor of the crater 
is hummocky— a jumble of domes and hills with numerous 
cracks and rocky blocks, so that it may represent a kind of 
double-ring crater. The walls are incomplete, so that either 
they have been destroyed or else they were never formed. This 
marked morphological difference between the inside and the 
outside of the crater suggests that it was formed by a quiet 
process rather than by violent impact. Craters with lobate lava 
fields and those with rough floors may lie, in the crater 
sequence, between the 'lunar' type and the Tharsis Tholus 
dome. 
138 



CRATERS ON MERCURY AND MARS 




Figurt 4. Arsia Moris 



This morphological sequence of craters suggests a gradual 
change of volcanic activity, from the fissure eruption to the 
central eruption, which may be associated with the gradual 
evolution of the crust— thin and soft at first, hard and thick 
later. The thin primitive crust would be easily fractured into 
tectonic plates by mantle convection and other subcrustal 
processes. Then, by the escape of the volatile components of 
the magma through tectonic fissures, the underground pres- 
sure would be reduced, so that there would be subsidence of the 
block plates. According to the endogenic hypothesis, this 
happened during the formation of lunar craters. 

As the crust thickened, the volcanic activity would change 
from fissure eruptions to the central gas and magma eruptions; 
the crater would become smaller, and become circular rather 
than polygonal. During the last stages of crustal development, 
the crust itself would be hard enough to support a magma 
reservoir, and cinder-cones and strato-volcanoes would be 
built up, as on Earth. In this respect the Martian crustal 
features are particularly interesting. The Noachis-Aeria high- 
land deserts are covered with lunar-type craters, while craters 
are lacking in the Amazonis and Tharsis deserts; instead, we 
find strato-volcanoes and volcanic domes with large vents. In 

139 



1978 YEARBOOK OJ- ASTRONOMY 




Figure 5. A rand as 



general, the Martian crust may be in an intermediate stage of 
evolution more advanced in Amazonis than in Noachis. 

The similarity of Mercurian craters to those of the Moon 
suggests that the crust of the planet is in the same stage of 
evolution. On Mercury, many of the craters have well-deve- 
loped central peaks or double ring structures, and some of 
them are surrounded with lava fields. 

One characteristic of the lunar scene, though not on Mer- 
cury, is the so-called beak pattern. Most of the lunar craters, 
except those in the polar regions, have walls broken at their 
north and south points, and the outer walls there extend away 
from the craters, swelling up in a north-south direction. 
Typical beak patterns are associated with Alphonsus and 

140 



CRATERS ON MERCURY AND MARS 




Figure 6. Yuty 

Arzachel. This suggests global appression in an east-west 
direction at the time of crater formation. J. E. S purr attributed 
it to the shrinking of the Moon by the escape of volatiles. 

On Mercury the beak patterns are less conspicuous, though 
the numerous scarps suggest that appression took place there 
also in milder form. The mean density of Mercury is greater 
than that of the Moon, and comparable with that of the Earth, 
so that there is certainly a metallic core; the gaseous content 
may be less. 

The origin of craters on terrestrial planets is still a matter for 

Ml 



1978 YCARUOOK OF ASTRONOMY 




figure 7. Cralcr in Cydonia 



debate. According to the impact theory, the basic cause is 
bombardment by meteoroids or asteroids, together with subse- 
quent volcanic activity to account for the lava-flows and the 
heterogeneous chemical composition of the materials. We 
must also consider the craters on the two dwarf satellites of 
Mars, Phobos and Deimos, which were discovered by Mariner 
9 and have been more closely studied by the Viking orbiters. It 
has been generally assumed that these craters are of impact 
origin, and certainly we cannot expect that small bodies of this 
kind would possess enough internal energy to produce craters. 
However, it is possible that craters could be formed, during the 
cooling stages of Phobos and Deimos, by the effects of a 
second 'boiling'. With a mixture of water vapour and liquid 
silicates, a decrease in temperature would result in the crystalli- 
zation of the silicates, together with a relative increase in 
vapour which would be soluble only under very high pressure. 
Further cooling and crystallization would induce ebullition, 
and therefore craters could be formed by the cooling of small 
satellites of the Phobos and Deimos class. 

142 



CRATERS ON MERCURY AND MARS 

Many craters on the Moon and Mercury, and craters and 
strato-volcanoes on Mars, are much larger than any corre- 
sponding formations on the Earth. Although Mars, the Moon, 
and Mercury are smaller than the Earth, so that presumably 
they have never had as much internal energy, the scale of 
landforms depends also upon the condition of the crust. If a 
lunar-type crater is basically the depression of a crustal plate by 
a decrease in underground gas pressure, its size would not be 
expected to be directly related to the amount of available 
energy. On Mars, gigantic volcanoes such as Olympus Mons 
could hardly be formed after the crust had thickened up. 
Finally, we must not forget that any high mountains and deep 
canyons on the Earth are affected by erosion and by crustal 
activity to a much greater extent than upon the other terres- 
trial-type worlds. 



143 



The Atmosphere of Mars; Past, Present 
and Future 

GARRY E. HUNT 

1 . Introduction 

The planet Mars has always interested astronomers, for it is 
the only member of our Solar System that superficially resem- 
bles the Earth. Early telescopes showed distinct markings that 
could be followed as they rotated with the planetary surface. 
The appearance of light orange and darkish grey-blue coloured 
areas that change on a seasonal basis and a disk crowned at the 
poles with brilliant white caps provided further information 
for early astronomers to speculate that the Earth and Mars 
were planetary twins. 

The space missions to Mars launched during the last decade 
have drastically changed our knowledge of Mars. From the 
Mariner 4 mission, the planet appeared bleak and moonlike 
and the surface pressure on Mars was found to be less than 1 
per cent of the Earth's. This value is lower by a factor of 10 than 
that previously estimated from Earth-based observations. 
Mariners 6 and 7 space missions extended these observations. 
Optically thin hazes were seen above the limb in several places, 
although these hazes did not noticeably obscure the surface 
features during the period of encounter the atmosphere was 
free of these clouds. The light and dark markings were attrib- 
uted to some kind of atmospheric interaction with surface dust 
controlled by local topography. Even at this stage, Mars did 
not appear to be an atmospherically active planet. 

When Mariner 9 reached the planet on 13 November 197], 
and the Russian Mars 2 and 3 space probes on 2 December 
1 97 1 , the greatest dust storm in more than a century was raging 
on the planet, almost totally obscuring the surface. When the 

144 



THE ATMOSPHERE OF MARS 

storm cleared it revealed a totally new look to Mars; a 
geologically, meteorologically, and just conceivably biologi- 
cally active planet. Now a further dimension has been added to 
our understanding of Mars through the four Viking spacecraft, 
the two landers which safely touched down on Mars on 20 July 
1976 and 3 September 1976 respectively, complemented by the 
two orbiters. In addition to the search for life, Viking has made 
important discoveries related to the fundamental geophysical 
problems of the cause of the Martian channels, the nature of 
the polar caps, the size of the ancient atmosphere, which 
collectively help to provide a more complete understanding of 
the past, present and possibly the future of the Martian atmos- 
phere. 



table ] Physical Data 

Venus Earth Mars 

Mass(10 26 g) 48.7 59.8 6.43 

Mean radius (km) 6049 6371 3390 

Mean density (gem 3 ) 5.26 5.52 3.94 
Inclination of equator 

to orbit 3° 23.5° 25.2° 

Orbital eccentricity 0.007 0.017 0.093 
Length of year 

(Earth days) 225 365 687 
Period of rotation 

(days) -243 1.0 1.03 (=1 sol) 

Satellites 1 2 



2. Atmospheric Structure and Planetary Topography 

The atmosphere of Mars is thin compared with that of the 
Earth. The average surface pressure is in the neighbourhood of 
6 millibars (m bar) while a typical terrestrial value is 
1,013 m bar. Surface pressures are primarily a function of 
altitude which on Mars may vary widely through the topogra- 
ms 



1978 YEARBOOK OF ASTRONOMY 
table 2 Planetary Data 





Venus 


Earth 


Mars 


Distance from Sun (Gm) 


108 


150 


228 


Solar flux (wm~ 2 ) 


2597 


1370 


595 


Albedo 


0.71 


0.33 


0.16 


Cloud cover (%) 


100 


50 


6 


Effective temperature (K) 


244 


253 


216 


Surface temperature (K) 


730 


288 


216 


Scale height (km) 


4.5 


7 


10 


Main atmospheric gases 


co 2 


N 2 ,Q 2 


co 2 



phic features of spots, volcanoes, calderas and rift valleys. 
Typically higher values are found in depressed areas or basins. 
A pressure of 8.9 m bar has been determined spectroscopically 
in the Hellas Basin, which is centred at 40 degrees south and 
290 degrees west. The basin is approximately 1,800 km north- 
south and 2,200 km in an east-west direction with the eastern 
slope noticeably less steep than the west. It is also a region of 
meteorological importance since many of the global dust 
storms seem to start in this region. Some of the lowest 
measured pressures are 1 m bar at the summit of Pavonis 
Lacus (1 degree north, 1 13 degrees west) and about 1.5 m bar 
at the top of Arsia Mons (1 1 degrees south, 1 19 degrees west). 
The altitude of Arsia Mons is estimated to be 19 km and the 
average slope of the structure to be approximately 3 degrees. 
Mars posseses a very rough surface by terrestrial standards, 
with large variations in the surface topography to the extent 
that the surface relief of the planet is approximately equal to 
the atmospheric scale height. Numerical experiments of the 
general circulation of the Earth's atmosphere suggest that 
orography is fundamental for producing the more permanent 
atmospheric patterns. On Mars therefore, we anticipate the 
orography to play a major role in characterizing the atmos- 
pheric motions. 
Temperatures in the thin lower atmosphere of Mars are 



146 



THE ATMOSPHERE OF MARS 

much lower than those on the Earth. The average surface 
temperature is approximately 210°K. The temperature ranges 
from 132°K in the polar regions to about 220° K near the 
equator. The daytime values reach to almost 250° K at the 
equator during the equinoxes. The coldest temperatures ever 
recorded anywhere on the Earth in the past few thousand years 
are higher than the average mid-latitude Martian temperature. 
The thin atmosphere will respond rapidly to the incident solar 
radiation, so that we may expect large diurnal temperature 
variations which has been confirmed by the measurement 
made by the Viking landers in Chryse and Utopia regions. 
There are currently the most distant meteorological stations in 
the Solar System. In the Chryse region, the Viking experimen- 
ters find a maximum temperature of 24 1.8° K occurs at + 1500 
local lander time (LLT) and the minimum of 187.2° K occurs at 
+0500 LLT, shortly before sunrise. These variations are much 
larger than we find on the Earth during the course of a day. For 
example, China Lake, which is part of a broad, dry basin in the 
Mojave Desert, California, the temperature variation is from 
292° K to 3 1 1 ° K, although the times of temperature maximum 
and minimum are the same at both the Martian and terrestrial 
sites. The similarity in times of maximum temperature can be 
explained through the dominant heating mechanism near the 
surface being convective transfer from the ground. The maxi- 
mum temperature is reached when the ground temperature has 
cooled enough so that convection effectively ceases. This 
occurs about 15.00 local time on both planets, since the 
atmospheric heat capacity and the rate of convection are both 
proportional to the air density. Consequently, the time of 
maximum air temperature is approximately independent of 
the air density. 

The polar caps on Mars have been a source of fascination 
since the first telescopic observations of the planet. Scientifi- 
cally, they play a very important role in the meteorology and 
climatology of the Martian atmosphere. The northern polar 
cap has a polygon shape and extends to about 60 degrees 
latitude at maximum. The measurements from the orbiting 
Viking spacecraft during the northern summer showed that the 



147 



1978 YEARBOOK OF ASTRONOMY 

residual cap has a temperature of about 205° K and an albedo 
of nearly 43 per cent. This temperature was high enough for 
any carbon dioxide to evaporate from the surface. Further- 
more, the Viking measurement found that the water vapour 
concentrations were a maximum over the residual north pole. 
There now seems little doubt that the residual pole is composed 
of dirty water ice, which has important implications regarding 
the future climate of Mars. The south polar cap is perennial in 
nature, and at its maximum extends as far as 50 degrees south. 
This is further than the north polar cap as a consequence of the 
longer southern hemisphere winter, but the transient cap 
extension is quite thin. The Viking measurements of the south 
pole in winter were equally unexpected, since a minimum 
temperature of 132°K was observed. This is more than 10°K 
colder than expected, and therefore below the C0 2 condensa- 
tion point at the surface pressure of the neighbourhood. The 
observation implies that the annual atmospheric condensation 
is less than previously assumed, and that either thick C0 2 
clouds exist at the 20 km level or that the polar atmosphere is 
locally enriched in non-condensable gases. 

Both polar regions show evidence of laminated terrain which 
extend to about 70 degrees latitude and resemble stacked 
plates. The uppermost layer being the permanent cap deposit. 
There is now strong evidence to suggest that these laminae 
indicate climatic cycles on Mars with each layer formed during 
a particular epoch. 

3. Atmospheric Composition 

The thin Martian atmosphere, probably formed principally 
from the emission of gases by the giant volcanoes which lie 
along the Tharsis ridge, is mainly composed of carbon dioxide 
with traces of water vapour, carbon monoxide, oxygen, ozone, 
argon, nitrogen, krypton and xenon. The minor constituents, 
argon, nitrogen, krypton and xenon are extremely important 
discoveries which provide invaluable information on the 
ancient Martian atmosphere which we discuss in the following 
section. The abundances of H 2 0, 3 and 2 are all extremely 
variable with both season and geographical location. 

148 



THE ATMOSPHERE OF MARS 
table 3 Composition of the Martian Atmosphere 





Abundance (%) 


Carbon dioxide 


95 


Carbon monoxide 


0.16 


Oxygen 


0.1 to 0.4 


Nitrogen 


2to3 


Argon 


lto2 


H 2 


Variable 


Ozone 


3 X 10" 6 


Krypton 


30X10" 6 


Xenon 


< 1 X 10" 6 



Upper limits of gases not detected in the Martian atmosphere 
Present upper limit Expected value 
Methane 120ppm 25 ppm 

Ne 10 ppm 5 ppm 

Ozone has been detected in the Martian atmosphere during 
both the Mariners 6/7 and Mariner 9 missions, although the 
amount detected is only 3-57 yum atm which is less than 1 per 
cent of the amount in the Earth's atmosphere (0.3 con. atm). In 
the summer, the amount is less than 3 jum atm, increasing in 
autumn in association with the polar hood until a maximum 
amount is found in winter. In 1971/72 this corresponded to 
57 yum atm over the polar hood and 16 /im atm over the polar 
cap. In the spring, the amount over the polar cap was found to 
decrease monotonically until at the beginning of the summer, 
the ozone has disappeared. Throughout the Mariner 9 mission, 
ozone was not observed in the equatorial region. 

The ozone in the Earth's stratosphere acts as a shield to the 
harsh U V rays of the Sun, which would be harmful to all forms 
of life, both human and animal, which reside on the surface. 
But on Mars, the limited amount of ozone is a poor barrier, so 
that UV rays of light at wavelengths as short as 1,900 A are 
known to reach the planetary surface. It is possible that these 
rays play a major role in photocatalytic reactions that convert 
the red iron oxide coating of the surface into a superoxidized 

149 



1978 YEARBOOK OF ASTRONOMY 

state. The superoxide surface, although a very powerful oxidiz- 
ing agent, could destroy organic molecules. But this does not, in 
itself, preclude the presence of life which could always reside 
under the soil or in more sheltered places, rather than on the 
hostile surface of the planet. 

The amount of water vapour in the Martian atmosphere 
(and also on the planetary surface) has always been a subject of 
speculation and debate, although recent Earth-based observa- 
tions have confirmed its geographical and seasonal variation. 
The Viking observations have added further dimensions of the 
diurnal variation and high spatial resolution of these import- 
ant measurements. They show very little water vapour in the 
Mars atmosphere in the southern hemisphere (0 to 3 pr ^tm) 
with a gradual increase across the equator to northern lati- 
tudes. A value of 30 k/j.m was observed in the Elysium-Amazo- 
nis region early in the Viking mission. 

It is generally agreed that the water vapour is confined to the 
lowest layers of the atmosphere, which undergoes a large 
variation of temperature during a Martian day (sol). The 
sublimation of a layer of exposed ice deposited on the surface 
must be discarded as the direct source of the vapour observed, 
since its lifetime in the solid phase at dawn would be too short 
to give the observed slow increase in vapour. The rapid 
evaporation of the surface frost at sunrise could, however, be 
the initial source of a ground fog, whose subsequent evapora- 
tion would produce the observed increase in vapour. The 
diurnal variation of vapour from exposed surface ice that does 
not pass through a second condensation phase to form an 
atmospheric haze layer would characteristically reach a maxi- 
mum very early in the day. Ground fogs have been seen in 
canyon regions of Mars in many of the Viking photographs. 

The largest abundances of water vapour have been found in 
the latitude band of 70 degrees to 80 degrees north in the 
northern midsummer season, with values of more than 
80 pr nm. These values imply near surface atmospheric tem- 
peratures of about 204° K in the polar region which are 
incompatible with the survival of a C0 2 polar cap, which at 
Martian pressures would require a temperature of 150°K. The 

150 



THE ATMOSPHERE OF MARS 

summer residual ice cap (above 82 degrees north) and the 
fragmented patches of ice remaining in the band 70 degrees to 
80 degrees north are therefore, water ice. The amount of water 
represented by the polar ice caps is still in doubt. However, the 
thickness of the polar ice can be estimated from the scale of 
surface roughness, which the thickness must exceed in order to 
produce features visible in the orbital photography as extended 
regions of high albedo. It is estimated to be between 1 m and 
1 km thick, which if all released at once, is sufficient to cover 
the entire planet in 0.5 m of water! 

But is this the only potential reservoir of water on the planet? 
Is it possible for running water to have cut the channels 
observed? To answer these fundamental questions we need to 
know more about the ancient Martian atmosphere and the 
meteorological processes on the planet. 

4. Trace Constituents and the Ancient Martian Atmos- 
phere 

Noble gases and nitrogen discovered in the Martian atmos- 
phere provide fundamental information that indicates a much 
greater carbon dioxide atmosphere in the past. Since noble 
gases are chemically inert and are not removed from the 
atmosphere through chemical reactions, they provide direct 
evidence of the volatile compounds released from a planet 
during its evolution. Chemically reactive substances, such as 
water, carbon dioxide and to a lesser extent nitrogen, are less 
reliable indicators since they can be trapped in the surface 
through the formation of nitrates and carbonates. 

The Soviet space probe Mars 6 indicated that as much as 35 
per cent of the atmosphere may be composed of argon. But this 
is a gross overestimate, when Viking measured about 2 per cent 
at the surface of the planet (Table 3). The Majority is Ar 40 , 
produced from the radioactive decay of K 40 in potassium-rich 
minerals. A tiny fraction is Ar 36 , a non-radiogenic isotope 
which may be traced directly to the inventory of volatile 
compounds in the material that formed the planet. 

Two other noble gases, krypton and xenon, have also been 
discovered on Mars, with krypton the more abundant of the 

151 



1978 YEARBOOK OF ASTRONOMY 



table 4 Comparison of the isotope ratios in the 
Martian and Terrestrial Atmospheres 

Species Mars Earth 



n l 7n 14 


0.0064 to 0.0050 


0.00368 


C .3 /C 12 


0.0118±0.0012 


0.0112 


o'7o 16 


0.00189± 0.0002 


0.00204 


Ar 36 /Ar 38 


4to7 


5.3 


Ar 36 /Ar 40 


(3.636 ± 0.02) X10" 4 


4X 10" 3 


Xe 129 /Xe 132 


2.5(+2or-l) 


0.97 



pair. But what do these measurements, in addition to the 
important detection of nitrogen, tell us about the ancient 
atmosphere on Mars? It would seem very unlikely that Mars 
had a massive original atmosphere, produced, for example by 
accretional heating, which was subsequently reduced to its 
present state by extensive solar wind sweeping. If this were the 
case, we would expect the Ar 36 / Kr to be much lower than the 
value found in the Earth's atmosphere or in the primordial gas 
in meteorites, since the argon would be swept off more 
efficiently than krypton in the upper atmosphere where diffu- 
sion separation occurs. Since the Ar 36 /Ar 40 ratio is less on 
Mars than it is on the Earth by a factor of 10, this may suggest 
that Martian degassing is less complete than on its terrestrial 
counterpart. Furthermore, through a scaling of the Ar 36 /C0 2 
ratio of the Earth for Martian conditions, suggests that the 
ancient atmosphere may have been thicker with a surface 
pressure of about 100 m bar. 

But the nitrogen measurements provide stronger evidence of 
an even more abundant ancient atmosphere. The Viking 
measurements show an enrichment of nitrogen 15 over 
nitrogen 14 that appears to be due to a differentiation of the 
lighter isotope caused by a photochemical processes. At a 
maximum, the nitrogen measurement indicates that the carbon 
dioxide atmosphere could have reached a pressure as great as 
the Earth's (1 m bar). Then if all the volatiles had been released 
at once, the water could have covered the planet to a depth of 

152 



THE ATMOSPHERE OF MARS 

200 m, so that the deep dusty basins would then have been 
oceans. 

Thus Mars may be viewed as having degassed and produced 
a thick atmosphere early in its history. The arrival of this early 
atmosphere in turn may indicate that most of the volcanic 
activity on Mars took place three to four aeons ago. Certainly, 
in these eafry stages of the planet's history, water would have 
run freely on the surface of Mars. 

5. Martian Meteorology 

The weather systems of the terrestrial planets, Earth, Venus 
and Mars are driven by the Sun, where the fundamental 
external drive for their planetary scale circulations is the 
difference of insolation between equator and poles. However, 
the resultant temperature contrast between equator and pole 
varies greatly between the planets. In terms of mean atmos- 
pheric temperature, the contrasts now are less than 2 per cent 
for Venus, 16 per cent for the Earth and 40 per cent for Mars, 
while for an atmosphere in radiative equilibrium, the contrast 
should be close to 100 per cent depending upon the inclination 
of the rotational axis. 

table 5 Meteorological Data 

Venus Earth Mars 

Response time of the 

Whole Atmosphere (sees) 

Radiation 10 9 10 7 2X10 5 

Dynamics 3X10 4 3X10 3 5X10 3 

Surface conditions chemical liquid/ dusty 

equilibrium solid 

Cloud amount (%) 100 50 6 

Adiabatic lapse rate (k/ cm) 1.01X10" 4 9.7X10" 5 4.5X10" 5 ' 

Topography as fraction of 

atmospheric scaleheight 0.2 0.3 1.0 



153 



1978 YEARBOOK OF ASTRONOMY 

The most important single factor which controls the plane- 
tary climatology is probably the total mass of the atmosphere, 
which is proportional to the ground pressure. The radiative 
relaxation time is proportional to the atmospheric mass and 
only when it is short compared to the relaxation time for 
dynamical processes can the atmosphere be in radiative equili- 
brium, with large temperature contrasts between equator and 
poles. Otherwise, the planetary scale motions will play the 
dominant role in heat transfer and will tend to give rise to an 
atmosphere with little horizontal temperature contrast and an 
adiabatic lapse rate in the vertical. It is apparent from the 
relationship between the radiative and dynamical relaxation 
times given in Table 5 that the thin Martian atmosphere is 
closest to radiative equilibrium, while the massive lower 
atmosphere of Venus is under strong dynamical control. 

We have seen earlier that the lower Martian atmosphere 
undergoes large diurnal changes in temperature, and these 
changes give rise to strong diurnal wind systems. Some direct 
information has been obtained from the meteorological meas- 
urements made by the Viking landers on the surface of the 
planet. During the first 20 sols the mean wind velocity was 
from the south at 2.4 ms' 1 . These lower level winds are strongly 
controlled by the local topography, and the wind direction 
varies throughout the day. During this initial period the winds 
remained light, and daily reproducible, with velocities less than 
8 ms" 1 , far below those of at least 30 ms" 1 necessary to raise the 
surface dust in the global storms. However, a major difference 
between Mars and Earth is that tidal winds are not very 
important in the terrestrial troposphere, but they are an 
essential feature of Martian meteorology. 

The weather systems in the middle latitudes of the Earth are 
a product of the global circulations. On a rapidly rotating 
planet heated more at the equator than the poles, coriolis 
forces give rise to westerly winds at higher levels. If the equator 
to pole temperature gradient is large, these strong zonal winds 
develop wave-like instabilities with which are associated high 
and low pressure weather systems. These instabilities are more 
intense in winter than summer because the temperature con- 

154 



THE ATMOSPHERE OF MARS 

trast between equator and poles is greater at the winter sol- 
stice. 

How does the Martian atmosphere behave? The winter 
hemisphere conditions are similar for Mars and the Earth, so 
we expect similar circumstances to prevail. Indeed, during the 
Mariner 9 mission, at a time near to the northern winter 
solstice, parallel bands of clouds were seen moving south- 
eastwards at 500 km/ day developing an east-west orientation 
at 41 degrees north. This behaviour, and the appearance of the 
clouds, are similar to a terrestrial cold front. The planetary 
weather systems may differ in the summer hemisphere. The 
axial tilt of both allows, at the solstice, slightly more insolation 
in the summer polar regions than at the equator. The relatively 
dense and cloudy terrestrial atmosphere provides a high 
reflectivity in the polar regions so that Jess solar radiation 
actually reaches the ground at the poles than the equator, even 
in mid-summer. But, for the transparent Martian atmosphere 
the reverse gradient may exhibit itself. The prevailing winds are 
then easterly, and light, with the absence of the usual planetary 
waves and little in the way of weather. The dominant wind 
systems should then be the tidal winds, which is precisely the 
situation found in the initial Viking surface observations made 
during the northern summer. 

Although, the Martian atmosphere is thin, it does possess 
layers of condensate clouds, which serve as tracers and modifi- 
cators of the weather systems. Earth-based observations and 
the early space missions had indicated the presence of bright 
patches in certain regions of the planet, such as in the Tempe 
ridge. But there was little evidence to suggest that Mars could 
possess such a rich variety of cloud types and activities that 
have now been identified. 

Water-ice clouds have been observed at levels as high as 50- 
60 km above the surface of Mars during the Mariner 9 mission. 
Clouds have also been found at about the 0.02 m bar level 
which is a comparable pressure level at which noctilucent clouds 
form in the Earth's atmosphere. Examples of lee wave clouds, 
convective roll systems, and layer clouds have all been 
observed in the Martian atmosphere. 

155 



1978 YEARBOOK OF ASTRONOMY 

The most prominent condensation clouds are seen poleward 
of 45 degrees in each hemisphere and these observed diffuse 
brightenings are known as the north and south polar hoods, 
respectively. They occur regularly in the period between winter 
and spring equinox. The Viking measurements have shown 
that the atmosphere over the residual northern polar region is 
saturated with respect to water vapour. Therefore, as the 
season progresses towards the cooler winter period, we may 
expect water vapour clouds to form in these regions. Conse- 
quently, it would seem that the clouds in the polar hood regions 
are composed of H 2 ice. 

The influence of topography may be the cause of cloud 
formations near the summits of some volcanoes, and the 
Viking pictures of clouds around Olympus Mons are a striking 
example. Certainly there is no need, nor any evidence to 
postulate that the volcanoes are active, to explain these obser- 
vations. These clouds are believed to be water ice since the 
temperatures are not low enough for condensation of carbon 
dioxide. Both orographic uplift and afternoon convection may 
contribute to these cloud formations. Since these features form 
in the vicinity of volcanoes, there may be local degassing of 
water vapour from the surface layers. 

In spite of its thin atmosphere, Mars clearly exhibits some 
fascinating meteorology with some similarities and interesting 
differences from terrestrial weather systems. 

6. Local and Global Dust Storms 

Flaugergues suggested that ochre-coloured veils were the 
cause of certain observations of Mars during the period of 1796 
and 1809, and his observations may be the earliest record of the 
yellow clouds or storms. Though they have been reported at all 
Martian seasons, global disturbances only seem to occur 
during the late spring and summer in the southern hemisphere. 
They appear when Mars is near perihelion and when the 
diurnal track of the subsolar point on the planet has reached its 
maximum southern latitude of 24 degrees. The clouds seem to 
germinate in specific areas in the southern hemisphere such as 
the Hellaspontus, Noachis, and Solis Lacus regions, which are 

156 



THE ATMOSPHERE OF MARS 

known to be elevated plateaux situated between 20 and 40 
degrees south latitude. 

In recent years, major storms have occurred in 1956, 1971 
and 1973, lasting for periods of 3-4 months. Fortunately for 
atmospheric scientists, Mariner 9 went into orbit around Mars 
and the Soviet Mars 3 spacecraft landed on the planet during 
the 1971 storm. These observations have provided us with a 
wealth of information from which we have been able to 
develop some understanding of this strange phenomenon. 

The development of the planet-wide storms seems to follow a 
well-defined pattern. In the initial phases lasting about five 
days, the storm appears as bright spots or cores with diameters 
of less than 400 km which undergo some diurnal regeneration 
and overnight decay. The storm then appears to grow, initially 
in an east-west direction, while blue-white peripheral clouds 
may appear. Secondary cores may also develop at new loca- 
tions during this phase of the storm which may last for a 
period of 5 to 20 days. In 10 to 20 days, the planet is encircled 
and planetary obscuration occurs in 20 to 30 days in the cases 
when this stage is reached. The lifetime of the storm will vary 
according to the meteorological conditions which prevail at the 
time, but when it begins to decay, the clearing is first noticeable 
over the polar regions and the high volcanoes. 

But why should the thin Martian atmosphere exhibit the 
violent change in its local meteorological pattern? What special 
conditions trigger these storms? The Martian atmosphere 
does, of course, possess a background level of dustiness with 
the maximum dustiness occurring during the southern spring 
and early summer. Indeed, the pictures taken from the surface 
of the planet show a pink rather than a blue sky, confirming 
this result. The blue sky of the Earth's atmosphere is caused by 
the Rayleigh scattering of sky light by the air molecules. On 
Mars, there is insufficient air density for there to be an 
appreciable Rayleigh scattering. However, the dust particles of 
about 0.1 fxm in size suspended in the Martian atmosphere 
scatter the incident sunlight at longer wavelengths than any air 
molecule, which accounts for the pink sky we observe on Mars. 
The dust particles are highly absorbing, composed of a 50 ± 10 

157 



1978 YEARBOOK OF ASTRONOMY 

per cent Si0 2 content of the Martian surface material, which is 
further evidence for a geologically active and differentiated 
planet. 

The global distribution of light albedo markings which trail 
from craters and other topographic obstacles are a direct 
indication of wind-blown dust on Mars. Strong local winds 
generated by the huge elevation differences and the short 
radiative time constant indicate that the threshold to raise the 
dust from the surface of the planet may often be exceeded. The 
strong mid-summer solar heating will cause global scale winds 
of sufficient magnitude for this purpose. The initiation of the 
storm may be due to the superposition of one or more 
additional wind systems on top of a meridional circulation 
which is already strong. Since the north-east portion of 
Noachis is a favoured region for storm generation, the topo- 
graphy of that region is probably an essential ingredient. The 
large temperature difference of about 80° K between the 
retreating polar cap and the adjacent ground would produce a 
local mechanism for increasing the level of atmospheric dust at 
this time. Dust devils and local cyclonic dust storms, familiar 
properties of terrestrial desert regions, are expected to be 
ubiquitous on Mars, and they would serve as mechanisms by 
which low levels of dust could be created and maintained in the 
southern hemisphere. The strong solar heating of a local dust 
pall in the presence of weak cyclonic swirl or vertical motion 
may create horizontal temperature gradients which then 
induce strong vertical motion. This is a type of 'dusty hurri- 
cane'. Heating rates as large as 25° K/ day can exist when dust is 
lifted off the Martian surface and into the atmosphere. There is 
then a strong feedback between the increased atmospheric 
heating and the wind systems. Through the hurricane mechan- 
ism, the dust heating produces high wind speeds which raise 
more dust and give rise to further atmospheric heating. As the 
storm continues, dust will gradually fill the atmosphere over a 
wide area, remove the horizontal temperature gradients and 
then cause the storm to decay. 

Hopefully, a dust storm will occur during the extended 
portion of the Viking mission which will help us to refine our 

158 



THE ATMOSPHERE OF MARS 

understanding of the mechanisms involved. But there is little 
doubt that the Martian dust storms are a violent meteorologi- 
cal phenomenon. 

7. Mechanisms for Climatic Change on Mars 

As a more comprehensive picture of the Martian environ- 
ment starts to emerge from the wealth of scientific data 
obtained from the recent space missions, we are still faced with 
providing an answer to the fundamental question; has running 
water ever existed on the surface of the planet? Although the 
erosion by a flowing liquid seems to be a natural explanation of 
many of the large and braided channel patterns observed by 
Mariner 9, the present atmosphere with a surface pressure of 
only about 6 m bar, is far too tenuous to permit liquid water. 
All the water presently on Mars must therefore be in the form 
of ice or vapour. 

The Viking images show examples of tear-drop shaped 
features that are unmistakenly ancient islands in sky stream 
beds, water sculpted terrain, and water lines along the shores of 
the channels. Their geomorphology would suggest that the 
channels have been cut by a fluid agent, and it is difficult to 
suggest an alternative to liquid water. Other images show 
channels that seem to emerge from the head walls of canyons 
just below regions of collapsed terrain. It is thought that these 
channels could be caused by slow seepage of underground 
water or wholesale melting of subsurface ice, which causes the 
collapse of the region where the water originated. 

Volcanic eruptions or meteorite impacts are possible 
mechanisms for the sudden release of large quantities of water. 
At least a dozen large volcanoes are quite prominent on Mars, 
and the amount of water released from them and the craters is 
of the correct order of magnitude to explain the channels. If a 
large quantity of water were suddenly injected into the atmos- 
phere it may stay there long enough to spread over the planet 
and rain out leading to widespread channel formation. But it is 
difficult to precisely estimate the ages of these volcanoes, and 
the current views range from 100 million to 1000 million years. 
Also, there is no current agreement on the ages of the channels, 

159 



1978 YEARBOOK OF ASTRONOMY 

although it is not thought they were all formed at the same 
time, but at intervals greater than 10 7 yrs. The best measure of 
channel ages is obtained from crater counts, which requires a 
statistical approach that may not be reliable until a large 
number of regions are analysed by the high resolution Viking 
images. 

Now there is little to debate about the aqueous environment 
of Mars, for Viking has found water in abundance in the 
neighbourhood of the poles and the mid latitude channels. We 
have seen that the northern polar cap may harbour a deep 
reservoir of water, while further quantities may be stored in the 
broken surface of the planet in the form of ice or permofrost. 
Certainly then, it would appear that the fracturing of the 
regolith by meteoritic impacts could indeed make the water 
permeate to the surface. Furthermore, it will be important to 
determine whether the polar reservoir of ice acts as a source or 
sink, over periods greater than a Martian year for the atmos- 
pheric vapour during this phase of the present epoch. 

But has the Martian atmosphere been thick enough in the 
past for large quantities to flow on the surface? Could such a 
situation happen again in the future? We have already seen 
from the isotopic inventory, and in particular the measurement 
of nitrogen (Table 4), that the ancient Martian atmosphere 
may have had a surface pressure as great as the Earth's current 
value of 1 m bar. While this situation certainly meets our 
requirements, could the Martian atmosphere even increase 
again from its current tenuous state? 

Observations of the layered deposits in the polar regions of 
Mars suggest evidence of climatic change on the planet. These 
laminae appear to be unique to the polar region, extend from 
both poles to about 70 degrees latitude and seem to consist of 
layers of approximately uniform thickness. Each individual 
layer may be no more than 50 m thick. What are the processes 
which form these laminae? Since the laminated terrain is 
unique to the polar regions it suggests a meteorologically 
controlling mechanism. The residue polar caps are now known 
to be water ice, although, the seasonally varying caps will 
contain deposits of carbon dioxide also. Direct evidence of the 

160 



THE ATMOSPHERE OF MARS 

atmospheric feedback on to the winter polar cap was obtained 
during the Viking meteorological measurements made from 
the surface of the planet. The decline in surface pressure 
recorded on the northern hemispheric site in the Chryse basin 
was a direct result of carbon dioxide being deposited at the 
south pole. The atmosphere-cap interaction would appear to 
be the controlling mechanism for seasonal variations of the 
surface pressure. As a result, the complete caps will contain a 
mixture of volatiles such as carbon dioxide, water and non- 
volatiles such as silicate dust deposited during the dust storms. 

How can these volatiles be released into the atmosphere? 
There are three important cyclic changes in a planet's move- 
ment which combine to produce a variation in the amount and 
distribution of solar radiation incident upon the planetary 
disk, but without affecting the integrated flux of heat received 
by the whole planet in a course of a year. They are the changes 
in the eccentricity of the orbit, the obliquity of the axis of 
rotation and the precession of the longitude of perihelion, 
Table 6, first discussed by Milankovich as an attempt to 
explain the timings of the terrestrial ice ages. Although the 
variation in the terrestrial parameters may appear small 
compared with those for Mars, they still provide large varia- 
tions in the radiation. For example, 10,000 years ago the 
eccentricity was 0.0190 (now 0.0167), the longitude of perihel- 
ion 102° (249°) and the obliquity 24.22 (23.45°), which caused 
a 7 per cent increase in the solar radiation for the northern 
summer solstice with a 3 per cent increase in the annual 
radiation at the poles. These changes in the incident radiation 
may have resulted in the surface temperature at the earlier 
epoch being higher than now by a degree or more globally. 
Since there now seems little doubt that "these astronomical 
perturbations to the Earth's radiation are responsible for 
initiating the advance and retreat of the terrestrial ice ages, this 
is a reassuring calibration before applying these ideas to 
Martian environment. 

The obliquity of Mars is highly variable with extremes of 15 
degrees and 35 degrees occurring over time periods of about 
10 5 years (Table 6). During these extremes the yearly insolation 

161 



1978 YEARBOOK OF ASTRONOMY 

table 6 Astronomical Factors Related to Climatic Change 



Earth Mars 



Obliquity 
Current value (°) 
Variability (°) 
Period (years) 

Eccentricity 
Current value 
Variability 



Period (years) 

Precession of the longitude 
of perihelion (years) 



23.4 


25 


±1 


±10 


4X10" 


1.2X10 5 




1.2X10 6 


0.013 


0.09 


+0.04 


+0.03 


-0.1 


-0.07 




10 5 


10 5 


2X10 6 


2.1X10 4 


1.75X10 5 



at the poles of the planet may vary by over 100 per cent. These 
obliquity variations of Mars are therefore large enough to have 
important climatic implications, since it would then heat up the 
poles and surface and release into the atmosphere any volatiles 
they contain. It had previously been thought that additional 
carbon dioxide was stored in the polar caps. The knowledge 
that the residual poles of water ice is a setback to rapidly 
increasing the thickness of the atmosphere, and therefore the 
surface pressure, by this method, since water vapour is a less 
effective constituent for this purpose compared with carbon 
dioxide. However, there may well be sources of carbon dioxide 
in the regolith at a depth of a kilometre or so below the surface 
layers, which may then be released into the atmosphere 
through the additional heating induced by the changes in the 
Martian 'astronomical parameters'. Certainly, then, Mars 
must have a very variable climate. The precise magnitude of the 
future surface pressure variations on Mars is currently not 
known and the possibility of the atmosphere being sufficiently 
thick for water to run freely on the surface remains an exciting 
speculation. 



162 



THE ATMOSPHERE OF MARS 

Summary 

The recent space missions to Mars, and Viking in particular 
have reshaped our knowledge and thinking of the atmosphere 
of Mars. The isotopic inventory provides direct evidence that 
the planet once had an Earth-size atmosphere with a surface 
pressure that may have reached 1 m bar. Under these condi- 
tions, the deep dusty basins would have the Martian seas. 
Water has certainly run on the planet to cut the channels which 
seem to be typical surface features at some localities. The polar 
caps may be reservoirs for this water, while amounts may also 
be locked up in the surface material. 

At this time, Mars has a tenuous atmosphere which is only 1 
per cent as dense as the Earth's. However, it is dramatically 
active with meteorological phenomena resembling features 
seen in the terrestrial atmosphere, and at the same time 
possessing its own brand of violent storms in the form of the 
global dust storms which shape the surface and modify the 
atmospheric environment. 

Mars today is cold and the atmosphere is too thin for liquid 
water to flow on the surface. But this may be a temporary state, 
since there is no doubt that the planet has a very variable 
climate, with far greater extremes, than we will endure on 
Earth. We still have a great deal to learn in order to obtain a 
complete understanding of our planetary neighbour and future 
missions to the planet have been stimulated by the data 
obtained during the Mariner 9 and Viking missions. These 
encounters have shown Mars not to be a dead planet, but 
geologically, meteorologically and just conceivably biologi- 
cally active. 

Acknowledgements 

It is a pleasure to thank my many colleagues, in particular Dr 
G. Briggs, Dr H. Masursky, Professors C. Leovy, M. McElroy, 
T. Owen and C. Sagan, for extensive discussions of Martian 
issues. 

References 
Readers interested in studying some of the detailed discus- 

163 



1978 YEARBOOK OF ASTRONOMY 

sions of the Martian atmosphere may wish to consult the 
following texts, which also contain extensive references: 

Hunt, G. E. A new look to the Martian atmosphere, Proc. Roy. Soc. A341, 317-330 
(1974). 

The Viking Results 
Science, 193,759-812(1976). 
Ibid., 194, 57-105 (1976) 
Ibid., 194, 1274-1352(1976). 



164 



Neutron Stars 



S. JOCELYN BELL BURNELL 



Ten years ago the most dense, compact type of star known was 
the white dwarf. The tiny, faint companions of Sirius and 
Procyon were the first stars found of this kind. They are old 
stars that have exhausted their nuclear fuel and subsequently 
contracted under the force of gravity. The matter of which they 
are made is not normal matter such as we are familiar with here 
on Earth. All the things we are familiar with consist of atoms, 
which in turn consist of a nucleus, which is very small and 
dense, surrounded at some distance by electrons. In a white 
dwarf star the outer structure of the atom has collapsed under 
gravity and no longer are the electrons well spaced around the 
nucleus, keeping apart the nuclei of separate atoms; the nuclei 
are closer packed than one would normally expect. A white 
dwarf of the same mass as the Sun would have a diameter 
about thirty times smaller than the Sun and would be so dense 
that a matchboxful of it would weigh a ton. 

Undaunted by the bizarre nature of white dwarfs, some 
theoreticians had speculated in the nineteen-thirties about 
collapse under gravity to even greater densities and to even 
more peculiar forms of matter. They suspected that if white 
dwarf material were compressed still more the positively and 
negatively charged particles in the atom (the protons and 
electrons) would combine to form neutrons — uncharged parti- 
cles, a number of which are found in the nucleus of every atom. 
They thought that this should be a stable form of matter. Thus, 
the white dwarf material would be turned into pure neutrons, 
the density of this matter being some ten thousand million 
times greater than that of the white dwarf. 



165 



1978 YEARBOOK OF ASTRONOMY 

Might there be stars made of this peculiar stuff, almost pure 
neutrons? Some astrophysicists thought that such neutron 
stars could exist, perhaps being formed in a supernova explo- 
sion, but since they would be extremely small and well-nigh 
invisible little attention was paid to the idea. Until 1967/8. 

Pulsars 

Thirty-odd years after this prediction a new radio telescope 
which I operated at the Mullard Radio Astronomy Observa- 
tory at the University of Cambridge inadvertently stumbled 
upon neutron stars. We were meant to be observing quasars, 
and were doing a systematic survey of the sky (or that part of it 
visible from Cambridge) picking out cosmic radio sources that 
showed rapid fluctuations— a form of twinkling. Because 
quasars have smaller apparent diameters than most other 
categories of radio source they should twinkle strongly. The 
telescope was also suitable, it turned out, for discovering 
pulsars— radio sources that emitted their radiation in pulses or 
flashes, typically at a rate of one pulse per second or half- 
second. We established that the sources of the pulses were 
outside the Solar System, but inside our galaxy, so that we 
were dealing with some sort of star; but this rate of one per 
second is uncomfortably fast for a conventional star, and 
difficult even for a white dwarf. As the data on these pulsars 
accumulated some key facts emerged. The pulse periods were 
very accurately maintained (comparable with the accuracy of 
an atomic clock in some cases): and the rapid fluctuations 
implied a very compact source, perhaps only a few kilometres 
across. A star could only maintain an accurate pulse period if it 
had large reserves to draw on, so that frequent emission of 
pulses did not appreciably deplete its store of energy and cause 
it to slow down. This implied a star of large mass. 

It is now realized that the radio pulsars are neutron stars— 
for neutron stars are both massive and very compact. The 
pulsing, or flashing, is believed to be due to the rotation of the 
neutron star, there being one pulse per revolution of the star on 
its axis. There is still no agreement about the exact way the 
pulse is produced: some astronomers favour the existence of a 

166 



NEUTRON STARS 

hot spot of some description on the surface of the star— each 
time this spot revolves we get a flash of radiation. Other 
astronomers point out that the neutron star will have a large 
magnetic field rotating with it and carrying around with it any 
material there may be at the surface of the star. Some distance 
away from the surface of the star this co-rotating material and 
magnetic field will be travelling at large speeds— speeds close 
to the speed of light. In regions such as this, relativistic effects 
are important and could concentrate radio emission into a 
beam. Whichever version is correct, the net result is that the 
neutron star behaves like a lighthouse, swinging a beam of 
radio emission around the sky several times a second. Each 
time the beam sweeps across the Earth we get a pulse. 

There are about 150 pulsars known today, and their periods 
range from 0.03 seconds to 4 seconds. They all emit radio 
pulses — that is how they have been found — but two of them 
emit pulses in other parts of the electromagnetic spectrum as 
well. It is probably no coincidence that these are the two fastest 
pulsars. In the centre of the Crab Nebula is the fastest pulsar of 
all — rotating some thirty times a second. From this pulsar 
flashes have been detected at optical wavelengths, at X-ray 
wavelengths, and at even shorter wavelengths too, in the 
gamma-ray region. The second fastest pulsar, in the constella- 
tion of Vela in the Southern Hemisphere, has recently been 
found to emit gamma-ray pulses; curiously no X-ray pulses 
have yet been detected from it, but optical astronomers in 
Australia identified it in early 1977. 

Binary X-ray Stars 

X-ray astronomy is one of the newer branches of astronomy; 
it is technically difficult because the Earth's atmosphere 
screens us from the X-rays from space, so all X-ray astronomy 
has to be done with telescopes flown high on rockets, satellites 
or balloons. The first X-ray astronomy satellite was launched 
in 1970, and amongst the sources it discovered and studied 
there were some particularly intriguing ones in the Milky Way 
which showed periodic variations in their X-ray emission. The 
source known as Centaurus X-3 (the third X-ray source 

167 



1978 YEARBOOK OF ASTRONOMY 

identified in the constellation of Centaurus) is typical of these. 
Its X-ray emission is strongly pulsed— about 80 per cent 
pulsed— and it has a pulse period of 4.84 sees. As well as this 
there is another period of 2.087 days in the data; for about half 
a day in every 2.087 Cen X-3 is considerably weaker (by a 
factor 10) than it is for the rest of that period. The 4.84 sec 
pulsation cannot be detected on these half-day holidays! To 
further confuse the issue, sometimes the source remains invisi- 
ble for weeks at a time, when neither the 4.84 sec nor the 2.087 
day periodicities can be seen. Careful examination of the 4.84 
sec pulsations revealed that the period actually changes, 
ranging from 4.83 to 4.85 sec, and this change was also cyclical, 
with a period of just over two days! 

To date there are about a dozen X-ray sources which show 
this sort of behaviour: their pulsation periods are between one 
second and several hundred seconds, while the other, longer 
periods are in the range one to ten days. These sources are 
believed to be binary systems in which a large B star (a blue 
supergiant) and a neutron star orbit each other. The two stars 
form a particularly close pair, and the gravitational pull of the 
neutron star distorts the supergiant and pulls material off it (at 
a rate of 100 million million million tons per second). This 
accretion of material by the neutron star is the key to the X-ray 
emission which arises when the material is funnelled down on 
to the neutron star's surface by its magnetic field. The binary 
system has an orbital period of several days, and once per 
orbital period the neutron star (and X-ray emission) is eclipsed 
by the supergiant. The period on the time scale of seconds is the 
rotation period of the neutron star — as in the radio pulsars we 
receive one flash per revolution. The small cyclical changes in 
the X-ray pulsation period are the Doppler shifts produced by 
the orbital motion of the neutron star around its supergiant 
companion. This tidy picture is spoilt by the anomalous lows — 
the days or weeks when no X-ray emission is detectable from 
the source. These phenomena are believed to be due to changes 
in the rate at which material is accreted from the large star by 
the neutron star, but it is not clear whether there is a halt in the 
accretion and therefore no X-rays, or whether there is an 

168 



NEUTRON STARS 

increase in the accretion and no X-rays because the extra 
material around the neutron star absorbs them. 

Supemovce 

Supernovas are cataclysmic explosions which mark the 
death of some larger stars. When they occur in that part of the 
Milky Way close to us they are very spectacular— the explod- 
ing star may become as bright as the full moon, and be visible in 
the day-time for days or weeks, then gradually fade. Astrophy- 
sicists have estimated that on average there is a supernova 
explosion in our galaxy once every 50 or 100 years, but as luck 
would have it, one has not been seen since 1604 (shortly after 
the death of Queen Elizabeth I, and before the invention of the 
telescope!) 

A supernova does not occur until the star has used up much 
of its available nuclear fuel, so in that sense it is an old star, but 
because these stars are big and massive they burn more rapidly 
and more quickly reach their dramatic end. Much of the star is 
blown off in the supernova explosion but the core of the star 
remains, and it is this core that in the explosion becomes 
compressed to form the neutron star. 

However, we may soon have to consider other methods of 
forming neutron stars. Although only 150 pulsars have been 
detected so far, there are estimated to be 100 thousand or a 
million active pulsars in our galaxy. Each has a life expectancy 
of some million years before so much of its rotational energy is 
used up that it can pulse no more. If these estimates are correct, 
then there would have to have been, on average, one supernova 
explosion every ten years in our galaxy. Perhaps neutron stars 
can be formed quietly— perhaps the contraction which must 
occur when a star runs out of nuclear fuel and ceases to shine 
can proceed steadily without the outburst of energy which 
causes the supernova. 

The binary X-ray stars have probably also been through a 
supernova stage, but here the picture is more involved because 
there are two stars to consider. A probable scenario looks like 
this: in the beginning there is a binary system consisting of a 
large star and a very large star. The very large star evolves 

169 



1978 YEARBOOK OF ASTRONOMY 

rapidly and after a million years or so has used up its fuel and 
explodes as a supernova forming the neutron star. Its compan- 
ion which has been evolving more sedately now finds itself 
sharing life with a very compact neutron star, and instead of 
being the smaller star in the binary, it is now the larger— by far. 
At this stage we have the typical X-ray binary described above. 
What stages might follow? In the immediate future the neutron 
star will quietly accrete material from its larger partner which 
must, of course, be evolving itself. As this evolution proceeds 
the rate of transfer of material to the neutron star varies— the 
variation will probably show up as changes in the rotation rate 
of the neutron star, and as changes in the X-ray brightness. 
Ultimately, the larger star will have burnt up all its nuclear fuel 
and presumably will go through a supernova stage to form a 
neutron star. Provided this explosion does not disrupt the 
binary system, we would then have two neutron stars orbiting 
each other. 

The Binary Pulsar 

One astrophysicist has estimated that about 1 per cent of all 
pulsars should be in such a binary system. He made the 
prediction when 1 10 pulsars were known, and soon after that 
the first binary (radio) pulsar was found. This pulsar, known as 
PSR 1913 + 16, was first detected in July 1974, and found to 
have a period about 59 milliseconds (59 thousandths of a 
second). Most pulsars change their periods slowly, by a few 
millionths of a second per year, as the neutron star loses 
rotational energy. But this pulsar wouldn't keep steady. It 
changed its period by up to 80 millionths of a second per day, 
and sometimes by as much as 8 millionths in five minutes! The 
explanation was in terms of a binary system, but a surprisingly 
fast binary, with an orbital period of about eight hours. This 
implies that the two components are very close together and if 
the other companion was an ordinary star like the Sun then the 
neutron star would be skimming its surface. The companion is 
probably another neutron star. 

As well as implying that our ideas about stellar evolution are 
broadly correct, this binary pulsar will be a useful check of 

170 



NEUTRON STARS 

relativity theory— according to that theory the orbit of the 
binary should show precession (just as the orbit of Mercury is 
predicted to show precession); the precession should be about 2 
degrees per annum. 

The Structure of a Neutron Star 

Apart from noting that neutron stars are orders of magni- 
tude more dense than white dwarfs and that they are composed 
largely of neutrons we have said little about what a neutron star 
actually is. Its mass is probably about the same as the mass of 
the Sun, but its diameter is only 20 kilometres (about 12 miles), 
so that it would fit comfortably within the boundaries of many 
of our cities. This mass concentrated in such a small volume 
means very large densities— on average 100 million million 
times as dense as water, or a thousand million tons per cubic 
inch. A pin's head made of this material would weigh more 
than the QE2. 

The neutron star probably has a solid crust, a liquid interior 
and perhaps a solid core. In some ways it resembles a raw egg — 
a thin shell on the outside and some peculiar fluids inside. The 
neutron star crust is relatively normal (note the 'relatively'). 
The density is only a million times that of water, and the crust is 
crystalline— mainly of iron. But not atomic iron— all the 
electrons have been removed and it is nuclei of iron atoms 
which are close packed. 

Inside the crust the density is greater and the substances 
more exotic. The next region, the mantle, is a fluid, made up of 
neutron rich materials. Here on Earth nuclei of atoms contain 
approximately equal numbers of neutrons and protons, and 
the largest nuclei which are stable have about 100 protons in 
them; above this number for some reason the nucleus breaks 
up. But in the neutron star mantle the number of neutrons is 
much greater than the number of protons, and nuclei with up 
to 140 protons are believed to be stable. The density in this 
region is about 1,000 million times that of water. 

Within the mantle is a superfluid core— a fluid almost 
entirely of neutrons, with a few protons and electrons around. 
This fluid has zero viscosity (there is no resistance to flow) and 

171 



1978 YEARBOOK OF ASTRONOMY 

is perfectly superconducting (there is no electrical resist- 
ance). 

What is inside this core is rather conjectural. Physicists do 
not yet understand the behaviour of material at very high 
densities and pressures. Perhaps the neutrons break down into 
even more fundamental particles— possibly the particles called 
hyperons, things like the 2", A° , A particles. This part of the 
neutron star has been described as 'a rich Greek alphabet soup'. 
Or perhaps at its centre the neutron star is a quark star. Quarks 
are particles that supposedly come in threes and have charges 
one-third or two-thirds of the electron's charge. They have 
been named after a phrase of James Joyce's 'three quarks for 
Muster Mark'. They have not yet been found to exist, although 
they have been searched for, so perhaps it is also appro- 
priate that in colloquial German quark means nothing, or 
rubbish! 

The gravitational force around a neutron star is very 
strong — objects on its surface would weigh ten thousand 
million times what they do on Earth. If there were the slightest 
wrinkle on the surface of the star the work one would have to 
do to get over it would be comparable to the work done 
climbing Everest. The gradient of the gravitational force is also 
much greater near a neutron star than it is near the earth. This 
means that if you went close to a neutron star there would be an 
appreciable difference in the gravitational forces on different 
parts of your body; your feet would feel a much stronger pull 
than your head for example, and the difference would be 
sufficient to pull you apart. Even curling up tight in a ball 
would not save you. 

As well as the strong gravitational field there is a strong 
magnetic field. It is believed to be about a million million 
gauss. To appreciate how large this is remember that the 
Earth's magnetic field (which is used in navigation by compass) 
is about one-third of a gauss. The largest magnetic field man 
can make is a few million gauss, and that can only be kept up 
for a fraction of a second. It is this enormous field that plays a 
crucial role in the production of the radio and X-ray pulses 
from neutron stars. 

172 



NEUTRON STARS 

In Conclusion 

All this sounds like science fiction, so incredible are these 
neutron stars. But regardless of the difficulty we may have in 
taking in the peculiar properties of these stars, they are here to 
stay, and astronomers are learning to live with them and to 
learn from them. Since the discovery of neutron stars fresh 
interest has been taken in the physics of matter at very high 
densities: there has been study of the atmosphere of neutron 
stars, the way in which they accrete material, and the way in 
which they radiate: and there has been more study of super- 
novas, where they are supposed to originate. There has been 
one other development in which neutron stars have played a 
large part, and this is because astronomers now ask themselves: 
if neutron stars exist, can even more compact, dense bodies 
exist? What happens if collapse under gravity continues 
beyond the neutron star stage? This has lead to the study of 
black holes, and compared with those of black holes, the 
properties of neutron stars look conventional! 



173 



Extragalactic Nomenclature - A Simple 
Guide 

SIMON MITTON 

The past few years have seen a considerable growth of interest 
in active and unusual galaxies, in addition to the widely 
publicized studies of quasars. There are several reasons for this 
burst of activity. The completion of several large telescopes, 
especially the 4-metre series now operating on Kitt Peak, in 
Chile, and in Australia, have spurred on researchers. Many of 
the peculiar galaxies are faint objects, due to their relatively 
large distance from the Milky Way, and hence a big telescope is 
essential for detailed studies. Another technological develop- 
ment has been the introduction of electronic, as opposed to 
photographic, techniques for the acquisition of data. For 
example, the instrumentation attached to a telescope such as 
the Anglo-Australian Telescope is much more efficient than 
would have been the case a few years ago. One remarkable 
invention of great value to spectroscopists has been the elec- 
tronic spectrum scanner; these devices enable the background 
light of the sky, containing auroral and streetlight contamina- 
tion, to be subtracted from the signal received from a star or 
galaxy. Since the night-sky emission lines are often stronger 
than galaxy or quasar emission lines the benefit to astronomers 
of sky-subtraction is very considerable. Added to these 
improvements in hardware has been the discovery of a great 
variety of phenomena in the extragalactic universe, all de- 
manding careful observation and critical theorizing. Since the 
most energetic and the most remote objects tend to be abnor- 
mal it is hardly surprising that a significant fraction of the 
usable time on the new telescopes has been allocated to those 
specializing on active galaxies. 

174 



EXTRAGALACTIC NOMENCLATURE— A SIMPLE GUIDE 

Rather like the botanists and stellar spectroscopists of a 
century ago, extragalactic astronomers like to be able to 
classify the objects that they look at. And, again like the 
botanists, terms are often invented before the true nature of a 
new object is fully understood. An unfortunate consequence 
for the amateur astronomer interested in galactic research is 
that there now exists a bewildering array of terms that are 
meaningless except to the experts. Common names such as 
Markarian galaxy or BL Lacertae object or Type II Seyfert 
actually convey no information to those not already familiar 
with the jargon. The confusion is compounded by the fact that 
some objects are named after their discoverer (e.g. Zwicky and 
Markarian galaxies) whereas others are categorized by their 
physical qualities (e.g radio galaxy or high-redshift quasar). In 
this situation, it is not unusual for an object to end up with two 
or three labels: some Markarian galaxies are Seyferts, for 
example. 

This lack of discipline in classifying extragalactic objects is 
not only bewildering when encountered for the first time, but it 
may even be hindering the progress of research if too much 
emphasis is attached to giving objects names, at the expense of 
understanding what makes them work. In those cases where 
objects are also radio or X-ray sources even more names will 
apply, because the source of radio emission has to be given an 
identifying tag before an optical object has been matched to it. 
Radio sources are frequently named after the observatory 
where they were discovered, whereas X-ray emitters tend to be 
named after the satellite carrying the X-ray telescopes. So, 3C 
273, is radio source number 273 in the third Cambridge 
catalogue, and A0620-00 is an X-ray star at right ascension 
06 hr 20 min in the Ariel satellite's survey. 

To provide a general guide through the minefield of extra- 
galactic nomenclature I have compiled the following brief 
notes. As new objects are found the boundaries between 
categories become less rather than more sharply defined. So 
there is a certain arbitrariness in the definitions and they 
probably will not agree exactly with those found elsewhere — 
there is more than one route through the minefield! 

175 



1978 YEARBOOK OF ASTRONOMY 

First of all I want to deal with some of the objects that are 
named after people. 

Zwicky compact galaxies were found by the astronomer 
Fritz Zwicky while working on Schmidt photographs of the 
deep sky. They are barely distinguishable from star images on 
the sky surveys. At first Zwicky circulated his lists privately, 
but they were later published. I Zw 1 denotes the first object 
listed in the first list (list I) and so on. In general, they are 
compact galaxies with a high surface brightness. 

Seyfert galaxies were first classified as a group by Carl 
Seyfert in 1943. They are spiral galaxies with brilliant nuclei 
and inconspicuous arms. The light from the nucleus has many 
emission lines of ionized gas. It is now known that the Seyfert 
galaxies are relatively common and the use of the term no 
longer indicates only objects given in Seyfert's original list. As 
a class they are subdivided into Type I and Type II. In the 
former category the lines of hydrogen in the spectrum have a 
much greater width than lines from the ionized metals, whereas 
in the second category they are of about the same width. If the 
spread of the line is interpreted as Doppler shifting, then the 
spread of velocities is thousands of kilometres per second in 
Type I Seyferts, but only a tenth of that in Type II. Many 
Seyfert galaxies are also radio sources, the most famous being 
NGC 1275 in the constellation Perseus, which is associated 
with the radio source Perseus A or 3C 84 and which is also an 
X-ray object. Another notable feature of the Seyfert galaxies is 
that they exhibit short-term fluctuations in the optical and 
radio outputs. This indicates that the active heart of some 
Seyfert nuclei cannot be more than a few light weeks in 
diameter. 

Markarian galaxies are named for the Russian astronomer, 
B. E. Markarian, who used a Schmidt telescope with a prism in 
front to net large numbers of objects with unusual spectra on a 
single photograph. A similar technique has been used very 
successfully on the UK 1.2-metre Schmidt telescope in Aus- 
tralia. Markarian's survey picked up many Seyfert galaxies as 
well as irregular and disturbed galaxies. 

Haro galaxies are essentially similar to Markarian galaxies, 

176 



KXTRAGAI.ACTIC NOMENCLATURE -A SIMPLE GUIDE 




Figure I. A group of interacting galaxies photographed with a [-metre telescope al 
Las Campanas in Chiie. The numbers refer to the IC catalogue of nebula:. IC4687 
may well be a type II Seyfert galaxy. IC 4686 has two compact nuclei that show 
emission lines, I he system is embedded in a gaseous envelope. The entire group is 
unique and needs further investigation. (European Southern Observatory) 

except that they were found in the southern sky by Haro, 
working at the Tonantzintla Observatory. 

In summary, it is only necessary to note that Zwicky, 
Markarian and Haro galaxies refer to objects in particular 
published lists, whereas Seyfert galaxies refer now (although 

177 



1978 YEARBOOK OF ASTRONOMY 




I'igure 2, The disturbed galaxy M82, which gives the appearance of having 
suffered a violent explosion. (Hale Observatories) 

not in 1 943) to particular physical types. 1 now want to mention 
those galaxies with a descriptive name. 

Exploding galaxies really do seem to be objects that have 
been overwhelmed by a nuclear catastrophe in the recent past. 
Perhaps the best known example in M82, the visible part of 
which consists almost entirely of ejecta thrown out I to 10 
million years ago. This object is also a strong radio emitter as 
well as an infrared source. 

N-type galaxies have almost all their luminosity concen- 
trated into a brilliant star-like nucleus that is surrounded by 
faint and compact nebulosity. In many respects they are very 
like the Seyfert galaxies, and the use of the term N-type seems 
to be dropping gradually. 

Radio galaxies, one of the oldest of the 'new 1 terms, are 

178 



EXTRAGALACTIC NOMENCLATURE-A SIMPLE GUIDE 




Figure 3. The spectacular ring galaxy known as the Cartwheel, photographed with 

the UK 1.2 metre Schmidt Telescope. The ring is composed ofhighly-excited gas. 

(UK Science Research Council) 



galaxies which emit a strong flux of radio waves. The proto- 
type of these objects is generally considered to be Cygnus A 
which emits a prodigious 10 3S watts in the radio domain. This is 
millions of times more than the radio emission from the Milky 
Way. Cygnus A is a distant 16th magnitude galaxy, visible only 
in large optical telescopes. The radio emission of radio galaxies 
generally comes from two elongated lobes symmetrically 
disposed on each side of the optical galaxy, which gives the 
superficial impression that energetic material has been thrust 
out of the galaxy in a symmetrical explosion. The very largest 
radio galaxies rival entire galaxy clusters in their overall 

179 



1978 YEARBOOK OF ASTRONOMY 




Figure 4. Another ring galaxy, photographed at the Kilt Peak National Observa- 
tory in the United States. (KPNO; AURA) 



extent. Radio waves are generated in radio galaxies by the 
synchrotron process: very high speed electrons in the source 
are constrained to move along curved paths by the internal 
magnetic fields, and this leads to the emission of electromag- 
netic waves. 

Ring galaxies have an apposite name because they look like 
rings. These objects have recently come to the fore because 
many of them have been found in the new series of surveys of 
the southern sky. Some of the rings have a central nucleus, and 
in some cases there is a small galaxy near to the ring along its 
axis of symmetry. It seems likely that a few of the ring galaxies 
were made when a spiral galaxy collided with a compact 

ISO 



EXTRAGALACTIC NOMENCLATURE— A SIMPLE GUIDE 

galaxy. This could trigger a burst of star formation and give a 
ring-like appearance. Other rings may just be spirals viewed 
from an aspect that makes the arms appear to form a ring. 
Certainly they are not a homogeneous class of objects and they 
would merit further study. 

Quasars (QSOs) are the most celebrated of the extragalactic 
oddities; the name is a contraction of quasi-stellar object. The 
first quasars found were starlike objects coincident with strong 
radio sources. The optical spectrum of a quasar usually has 
strong emission lines of substances such as hydrogen, oxygen, 
magnesium and carbon. The crucial property is that of red- 
shift: in the quasars the spectral lines are found at wavelengths 
considerably longer than for emission from objects at rest. The 
redshift is a measure of the change in wavelength relative to 
the rest wavelength. Quasar redshifts range from about 0. 1 up 
to about 4, with a great many in the range 1.5 to 3. Any object 
with emission lines, having a compact image on the sky survey, 
and a redshift exceeding about 0.4 will now tend to be classified 
as a quasar. A striking discovery of recent years is that some 
quasars do not emit radio waves at all and others have only 
absorption lines; hence the redshift is now the single most 
important quantity for categorizing an object as a quasar. 

BL Lacertoe objects (BL Lacs, not Lacertids as some extra- 
galactic astronomers unfamiliar with meteor showers will 
insist on calling them!). The first object in this category to be 
described was actually the variable 'star' BL Lacertae. This is 
actually a radio source bearing similarities to certain types of 
quasar. In addition, it is optically variable and has a strong 
polarization. The special optical property of BL Lacerta? 
objects is that they have a continuous power-law spectrum with 
no spectral lines or at best very weak ones. Most of the light is 
probably generated by the synchrotron process in a compact 
nucleus. Around two dozen BL Lacs are now listed in cata- 
logues. In a sense, they are quasars without any obvious lines in 
the optical spectrum. 

This is the very briefest 'user's guide' to extragalactic termi- 
nology. It is useful also to know a little about the various 
catalogues of radio and X-ray objects. To give a complete 

181 



I<)7X YEARBOOK OFASIRONOMY 




Figures. A BI. Lacertse object, 1400 + 162 which is apparently associated with a 
cluster of galaxies, (l.ick Observatory) 



listing of these would be long and tedious, so here is a note on 
the ones mentioned most frequently in the popular literature. 
Perhaps the one everybody knows is the 3C, or third Cam- 
bridge catalogue; there are also 4C and 5C listings. AH have 
been published in either the Monthly Notices or the Memoirs 
of the Royal Astronomical Society. The very extensive listings 
from the Ohio State Radio Observatory are preceded by two 
letters, the first of which is always O. Objects in the Parkes 
catalogues are denoted by the prefix PKS followed by four 
numerals giving the right ascension and two giving the declina- 
tion. Important X-ray catalogues include the Uhuru series, in 
which the code 2U and 3U precedes numerals giving the 
position, and the Ariel catalogue, which uses the letter A. 
Fortunately, observatories are now using a fairly uniform 
system to refer to newly discovered objects. Instead of assign- 
ing a number that gives the position in a list (e.g. 3C 273) it is 

182 



EXTRAGALACTIC NOMENCLATURE— A SIMPLE GUIDE 

now common to give a number that gives the position in hours 
and minutes of right ascension and degrees and tenths of a 
degree in declination. Thus, object 1400 + 162 (a BL Lac) is at 
RA 1600 hours and dec 16.2 degrees. This system makes it 
much easier to relate the same object in different listings. 

Observational and theoretical astronomers are moving 
closer to a uniform system of extragalactic taxonomy. Increas- 
ingly, the evidence is suggesting that there is a unity of the 
activity in galaxies and quasars. The amount of activity varies 
from object to object, but the names, which are little more than 
historical ballast, are tending to obscure this underlying unity. 
As examples note that in a great many respects the Seyferts can 
be considered as mini-quasars. And it is especially interesting 
that the spectra of low-redshift quasars and high-redshift 
Seyfert galaxies are often identical. If we imagine moving a 
Seyfert further away it is not hard to visualize that at some 
distance all we will resolve is the starlike nucleus, so the 
description would presumably then switch to the term quasar. 
Equally, some of the N-galaxies would look like quasars if they 
were only a little further away. Both Seyfert galaxies and 
quasars show optical and radio variability. Many quasars are 
indistinguishable with a radio telescope from radio galaxies. 

We see then that the properties of the objects thrown into 
boxes labelled 'Seyfert' or 'BL Lac', overlap to a great extent. 
How much more sensible it would be to call them all active 
galaxies, where the term galaxy would be understood to mean 
system of gas and stars of galactic mass beyond the Milky Way. 

Within the active galaxies an energetic nucleus is responsible 
for much of the observed phenomena. This nucleus probably 
contains a particle accelerator that is able to boost protons and 
electrons up to almost the speed of light, where their energies 
will perhaps be millions of times their rest energy. Various 
suggestions have been made for the ultimate energy source, 
and the problem cannot yet be considered as solved. Nonethe- 
less the field is narrowing, and many theorists now favour 
black holes as the ultimate energy source. A black hole is a 
region of space in which gravitation is so high that nothing, not 
even light, can escape. However, as matter falls into the black 

183 



1978 YEARBOOK OF ASTRONOMY 

hole it is able to release energy as electromagnetic waves under 
certain circumstances. If these special conditions do indeed 
prevail inside some galactic nuclei then black holes gobbling up 
stars and the interstellar medium would be prodigious sources 
of energy. Alternative ideas have been put forward, such as the 
hypothesis that the supernova rate might be unusually high 
inside a nucleus. If true, this would lead to an excess of energy. 
Even if the black hole model is accepted, however, it is still not 
known how the released energy is channelled into fast particles, 
nor how the high magnetic fields present in many objects are 
created. 

We can envisage that energy release from a central source 
will occur to different degrees in different types of object. 
Given this, we can now make a first crude attempt at systema- 
tizing extragalactic objects. In this picture the BL Lacertae 
objects have a strong flux of continuous light from the central 
source. This light has not excited any nuclear gas in a way that 
leads to emission lines and so the spectrum is featureless. In the 
quasars, on the other hand, there is plenty of gas around; this 
gets excited by the radiation from the black hole's neighbour- 
hood and emission lines result. Seyfert galaxies are sufficiently 
near that we can still see their spiral arms dimly beyond the 
brilliant nucleus. Similarly, in the radio galaxies it is possible to 
discern the underlying galactic structure. 

In this general approach we have not accounted for why 
some objects are funny while others are normal, because we do 
not know why this happens. Nor do we know how long an 
active galaxy can remain active. Either most galaxies go 
through this phase, in which case it is short-lived, or only a few 
do, but in those where there is activity it lasts a long time. Our 
instinct in these post-Copernican times is to assume that most 
objects are active at some stage, but that this must be tempor- 
ary for most of them. We know that in the past quasars, for 
example, were more numerous than they are now. So, are there 
any dead quasars in our vicinity? Again we cannot answer with 
certainty but there are intriguing clues. Unusual activity takes 
place in the centre of our own Galaxy: it seems to have thrust 
out a bit of a spiral arm recently and it is a strong infrared 

184 



EXTRAGALACTIC NOMENCLATURE— A SIMPLE GUIDE 

source. It has been suggested that the galactic centre may 
contain a small black hole to account for these observations. In 
the past this black hole could have been much more active than 
it is now. Perhaps in the future it may get stoked up again if 
sufficient stars drift too close to its irresistible clutches. So 
maybe even our own Galaxy has a mini-quasar in its heart. 



185 



What's New in the Local Group ? 



HEATHER COUPER 

You could be quite forgiven for believing that beyond the 
confines of our placid Galaxy, the Universe is a violent place. 
Super-luminous quasars blaze out from its remotest reaches; 
giant galaxies, racked with catastrophic explosions, send out 
distress signals of radio waves. Nearer home, we witness traffic 
accidents of gigantic proportions — galaxies slowly torn apart 
by the tremendous tidal power of a close encounter, their stars 
and gas flung into space in exquisite, convoluted streamers. 
But we tend to forget — much in the manner of sensational 
Sunday newspapers— that the majority of galaxies are quiet, 
law-abiding citizens. Most are so small and insignificant that 
they can only be studied close at hand; yet these are by far the 
most numerous galaxies in the Universe. It is fortunate indeed 
for our knowledge of normal galaxies that our Milky Way 
galaxy does not travel the Universe alone. It belongs to a small 
cluster of galaxies— the Local Group. As well as containing 
three, or perhaps four moderately large galaxies, the Local 
Group provides a home for a variety of smaller and fainter 
objects which would be unobservable if they were more 
remote. Only by studying our own small neighbourhood of 
intergalactic space can we get a true idea as to what really 
makes up the Universe. 

Clusters of Galaxies 

Clusters of galaxies, like our Local Group, are by no means 
unusual. Max Wolf identified a number of what he delightfully 
called 'nests of nebula?' in the opening years of this century; but 
the discovery of most clusters had to await the development of 

186 



WHATS NEW IN THE LOCAL GROUP? 

Schmidt telescopes in the early 1930s. At last, it became 
possible to photograph large fields of the sky — several degrees 
across — at once; and it was quickly noticed that the distribu- 
tion of galaxies looked clumpy. Astronomers today believe 
that over half the galaxies we see belong in clusters, whose 
member-galaxies are bound together in space by the invisible 
threads of each other's gravity. So tenacious are these forces 
that the largest clusters known are vast clouds of hundreds or 
thousands of galaxies, up to 50 million light-years in extent. 
These giant clusters uncannily resemble one another; in their 
size, their roughly spherical distribution of galaxies, and in the 
limited types of galaxies they contain. For this reason, astron- 
omers call them 'regular' clusters, and study their properties 
avidly; for these may be the basic 'building blocks' of the 
Universe. 

But what of the smaller clusters, like our own? Such 'irregu- 
lar' clusters have no particular distinction: they contain a 
hotch-potch of all galaxy types, from smooth ellipticals to 
lumpy spirals; there is no preferred distribution of members; 
and (with a few exceptions) they tend to be on the small side. 
'Small' is, of course, a relative term! The Local Group mea- 
sures some 5 million light-years from edge to edge; but our 
flattened cluster is clearly not in the same league as the giant, 
spherical, regular systems. Astrophysicists are currently trying 
to account for the differences between the two sorts of clusters; 
but it is a formidably difficult problem, requiring a knowledge 
of how galaxies form, evolve and interact in large numbers. An 
agreed picture has yet to emerge. 

If clusters of galaxies are common in the Universe, what 
about clusters of clusters of galaxies? It may seem rather an 
academic question, but it takes on more relevance when we 
learn that our Local Group is probably a member of one such 
'Supercluster' of galaxies. Detailed studies of the distribution 
of galaxies and clusters have revealed clumps of clusters up to 
180 million light-years across; and the consensus seems to be 
that these are real physical groupings. Our 'Local Supercluster' 
contains several other small clusters besides the Local Group — 
notably the M 81 group in Ursa Major, and the Sculptor 

187 



1978 YEARBOOK OF ASTRONOMY 

group — all centred on the giant swarm of galaxies in Virgo, 65 
million light-years away. However, the matter is not quite 
settled. Some eminent astronomers believe that the Local 
Supercluster is completely illusory, a result of the patchy 
clumping of galaxies. It is of vital importance to find the right 
answer, for astronomers need to know whether the motion of 
nearby galaxies is determined entirely by the expansion of the 
Universe, or modified by the gravity of the Supercluster. But 
this brings us to problems of cosmology, too remote to be 
considered here. It is time to return to the comparative 
neighbourliness of our Local Group. 

Our Local Cluster of Galaxies 

A distant observer studying our Local Group would hardly 
consider it worthy of the title 'cluster'. He might believe it to be 
just a pair of fine, well-matched spiral galaxies, accompanied 
by a smaller, rather patchier specimen. We ourselves know that 
the picture is different; but in order to get our bearings, let us 
briefly meet these important members of our neighbourhood. 

The smaller of the pair of spirals is a very special place to us; 
for it is our home, the Milky Way galaxy. At this point, we need 
not be too modest, for our Galaxy is a giant of its kind: a great 
rotating wheel of 100 thousand million stars, measuring 
100,000 light-years from rim to rim. Its hub is a densely-packed 
ellipsoid of old, cool red and yellow stars; and from this spring 
the spiral arms, threading their way through the Galaxy's disc. 
But unlike the solid spokes on a wheel, the glorious arms are 
evanescent. They are merely zones of compression, through 
which continually changing stars and gas slowly pass, and 
where star formation is triggered. As we see in other spiral 
galaxies, the arms are riddled with dust and gas, and studded 
with hot, young blue stars. It is to one such spiral arm, near the 
edge of our Galaxy, that the Sun and its planets currently 
belong; other arms nearby glow in our skies as the luminous 
band we call the Milky Way. 

Although our position in the Galaxy affords us magnificent 
views of young stars and shining nebulae, there is one serious 
disadvantage. Spiral arms are filled with tiny particles of 

188 



WHAT'S NEW IN THE LOCAL GROUP? 

dust — rather like cigarette smoke — which has the effect of 
blocking our view if we want to look into the galactic disk. As a 
result, light coming from the very centre of our Galaxy — and 
beyond — is dimmed thousands of millions of times. Although 
longer wavelength radiation, such as infrared and radio waves, 
can penetrate this murk, we know less about the nucleus of our 
own Galaxy than we do about others millions of light-years 
distant. But recently, astronomers have discovered an exceed- 
ingly small, powerful radio source right at our Galaxy's heart; 
and peculiar motions of gas nearby show evidence for a great 
explosion. Could our now-quiet Galaxy have been through a 
violent phase in its lifetime? Or are these motions simply telling 
us that our Galaxy is a barred spiral (with a bar-shaped, rather 
than ellipsoidal nucleus), as some astronomers believe? It is less 
perplexing to turn our attention away from the nucleus and 
into the region of space surrounding our Galaxy. 

But we have not yet escaped into true intergalactic space. A 
huge, near-spherical 'halo' of thinly spread stars surrounds our 
flat Galaxy, a relic of its very early days when it was a vast 
cloud of gas. As we would expect, this halo contains the objects 
which were the first to form — the oldest stars in the Galaxy. 
Many of these are concentrated into dense balls of thousands 
or even millions of stars, called globular clusters. We know of 
about a hundred such globulars in the halo, important histori- 
cally because they contain RR Lyrse variable stars which 
helped to fix the scale of our Galaxy. But some have lately 
taken on a new importance as the sources of intense outbursts 
of X-radiation — the mysterious 'X-ray bursters', recently dis- 
covered by orbiting satellites. Their mechanism is, so far, 
unexplained; but it seems that there is life in old stars yet! 

We have dwelt a long time on our Galaxy, for it is a very 
typical example and can give us standards to compare else- 
where. But it is time to move away, to cross the void of two 
million light-years which separates us from what may be the 
biggest galaxy in the Local Group; the Great Andromeda 
Spiral, M 31. In every respect, it appears to be a twin of our 
own Galaxy, but half as large again. Like our Milky Way 
galaxy, a radiosource marks its heart; its smooth nucleus is 

189 



1978 YEARBOOK OF ASTRONOMY 

wrapped in the coils of shining spiral arms; and over 300 
globular clusters throng its halo. 

Not far away from the Andromeda galaxy lies the third 
major member of our Local Group; the galaxy M 33 in 
Triangulum. A much smaller, fainter specimen, this; a clumpy 
little spiral with ill-defined, loosely wound arms. It is only half 
as large as our Milky Way; but with ten thousand million stars 
within its bounds, it is by no means a dwarf galaxy. 



4-5 



30 



1-5 



® 

IC342 






IC 10 
® 






#Moffell 






And I 






„„ \ M3I 185 

Audi!-*?' T^ 205 

. .£ \ M32 
AndU An i H 






® 
IC 1613 






Galaxy 




® 
Lao A 


® f»0j\Dra UMi 

"'VTs!xc W & 

Smc Lmc 

® 

6822 
, 1 to the centre 


Sex A 
® 




'" of the 

Seal, of 1 milJIm ligMy.or, J Loca( Superc(u5ter 

i i 1 



-30 -1-5 1-5 30 

(All galaxies without prefixes are NGC galaxies: eg, I85SNGC 185) I'Shtyears 

>V, Spiral galaxies ® Irregular galaxies •Elliptical galaxies 

Figure 1. The Local Group of Galaxies. 



190 



WHAT'S NEW IN THE LOCAL GROUP? 

Galaxies in Miniature 

Figure 1 shows how these three major galaxies fit into the 
Local Group. But you will notice that they have now been 
joined by a couple of dozen others, bringing the total member- 
ship up to about thirty. These are the small, faint galaxies 
mentioned earlier: the most common sort in the Universe. Just 
how different are these 'dwarfs' compared with larger galaxies 
like our own? Let us take a closer look. 

Dwarf galaxies come in two sorts, elliptical and irregular; so 
far, no dwarf spirals have come to light. Most diminutive of all 
are the dwarf ellipticals — marked as small black circles on 
Figure 1 — made up entirely of old, red stars. Their vigorous 
days of star formation are over; all their gas has long been used 
up, and they have settled into sedate old age. Most contain far 
less than a million stars and scarcely merit the title 'galaxy'; 
they are hardly more than globular clusters. But it is possible to 
tell the two apart, for the dwarf galaxies, although containing 
the same number of stars, are generally ten times larger; which 
means that their stars are very thinly spread. If we lived on a 
planet in one of these tiny galaxies, we would see only three 
stars in our night-time sky! 

Not surprisingly, dwarf elliptical galaxies — only 5,000 light- 
years across — are very hard to find. The majority have been 
discovered in the last thirty years during special searches 
around our own Galaxy and the Andromeda galaxy. Their low 
surface brightness makes them difficult to photograph; a task 
which is further complicated if they lie behind bright stars in 
our own Galaxy — such as Leo I and Leo II, which are very 
close to Regulus. The most recent search around the Andro- 
meda galaxy in 1971 added four new dwarf ellipticals to the 
Local Group; Andromeda I, II, III and IV. It is possible that 
Andromeda IV is not even a true dwarf, but a detached portion 
of the Andromeda galaxy itself. 

The ranks of these small elliptical galaxies have been further 
swelled by a few of their first cousins — true intergalactic 
globular clusters. These 'Tramp' globulars seem to have 
escaped from the gravity of their parent galaxies, and now 
roam the Local Group untrammelled. One globular cluster in 

191 



1978 YEARBOOK OF ASTRONOMY 

our own Galaxy — NGC 5694 — appears to be making such a 
bid for freedom, travelling away at a speed which is well above 
the Galaxy's escape velocity. Astronomers believe that the pull 
of passing galaxies may be responsible, just as massive planets 
can change the orbits of flimsy comets in our Solar System. 

Dwarf irregular galaxies (shown as ringed dots on Figure 1) 
are less shy about advertising their presence. These formless 
little clumps of stars can even be seen in other clusters of 
galaxies, and seem to be extremely common in the Universe. 
The biggest contain about a hundred million stars, making 
them some hundred times larger than the dwarf elliptical 
galaxies; but by contrast, these are luminous white and blue 
stars, blazing with the fires of youth. The dwarf irregular 
galaxies are unmistakably young, vigorous systems, rich in gas 
poised to form into generations of stars. And although the 
majority are relatively large, one of them has the distinction of 
being the smallest galaxy yet discovered. Shaped like a cosmic 
footprint, tiny GR 8 — only recently confirmed as a Local 
Group member — is only a thousand light-years across. 

Before leaving the realms of the dwarf galaxies, let us briefly 
consider the question of their distribution within the Local 
Group. A glance at Figure 1 shows that the dwarfs — especially 
the elliptical dwarfs — cluster in swarms about the giant galax- 
ies. Dwarf irregulars, on the other hand, tend to be fairly evenly 
spread. Why this should be is not yet understood; but theorists 
believe that it could be telling us much about the way galaxies 
form. 

The uneven distribution has prompted some astronomers to 
suggest that a giant galaxy and its retinue of dwarf ellipticals 
constitute a total system called a 'Hypergalaxy'. This, in effect, 
is a colossal Solar System, the giant galaxy taking the place of 
the Sun, with the dwarf ellipticals bound by its gravity in 
orbits, like planets. A few astronomers have gone so far as to 
say that the Local Group, as we understand it, does not exist; 
but is an effect arising from the closeness of two independent 
hypergalaxies — the Andromeda galaxy and our own. But as 
long as this remains an open question, we can continue to 
believe in the idea of a Local Group. Much work has still to be 

192 



WHAT'S NEW IN THE LOCAL GROUP? 

done on the motions of galaxies and the statistics of their 
distribution, before hypergalaxies become fact — if they ever 
do. There is, as yet, no compelling evidence that the dwarf 
galaxies around us are gravitationally bound to the Galaxy. 
They may well be making close approaches before winging off 
on orbits which will once again carry them into the depths of 
intergalactic space. 

Even the Milky Way's closest companions — the Magellanic 
Clouds — may not be permanent satellites. These two irregular 
galaxies are only 160,000 light-years away, appearing as 
glowing patches in Southern Hemisphere skies. They are by no 
means dwarf galaxies; even the Small Magellanic Cloud 
(SMC) has one-sixth the diameter of our Milky Way, while the 
Large Magellanic Cloud (LMC) is over a quarter as large. Both 
contain thousands of millions of stars and resemble the Galaxy 
in their rich and varied mixture of objects. The LMC is 
particularly similar, and its prominent central 'bar' of stars has 
led to suggestions that it may be a very clumpy barred spiral 
galaxy — and not an irregular, after all. 

The Magellanic Stream 

Like all spiral and irregular galaxies, the Magellanic Clouds 
are rich in cold, invisible hydrogen gas — the raw material of 
future stars. Its characteristic signal at 21 centimetres wave- 
length allows radio astronomers to map its distribution; and 
they have long known both Clouds to be embedded in the same 
giant cocoon of gas, believed to have remained from the days of 
the Clouds' formation. But recent work with the radio tele- 
scope at Parkes, Australia, has led to spectacular new develop- 
ments; the discovery of a huge intergalactic streamer of gas 
linking the Clouds to our Galaxy and stretching perhaps 
200,000 light-years into remote space in the opposite direction. 
Astronomers have estimated that this 'Magellanic Stream' 
contains a mass of gas equivalent to a thousand million stars — 
as much as the Small Magellanic Cloud itself. 

How did this colossal streamer arise? Some astronomers 
believe that an over-close approach by the SMC to our Galaxy 
some hundred million years ago caused vast amounts of gas to 

193 



1978 YEARBOOK OF ASTRONOMY 

be torn out of both systems. We see the evidence for such 
encounters throughout the Universe; distorted galaxies con- 
nected by ragged, broken filaments to each other. But the 
enormous tidal forces involved in this interaction would 
almost certainly have drastically separated the Clouds; and yet 
we see them still bound together in their 'foetal' gas. So the 
origin of the Stream is still a matter for speculation. Could it 
mark the orbital path of the Clouds, as some believe? Did it 
arise from collisions between the gas in the SMC and the 
unimaginably tenuous intergalactic medium? Many even more 
exotic theories will need to be tested before a consensus is 
reached. 

Hot on the heels of the discovery of the Stream came reports 
from other radio observatories of more intergalactic gas clouds 
and streamers. Jodrell Bank astronomers detected a cloud only 
one degree away from the Andromeda galaxy; another was 
discovered close to the galaxy, M 33. Great cloud complexes 
were found outside the Local Group in several nearby clusters 
of galaxies; in particular, the Sculptor group has some ten 
clouds associated with its brightest members. If these clouds 
are genuinely near the galaxies they lie close to in the sky — and 
there is no direct way of measuring their distances — then it 
seems certain that clusters of galaxies have a small, but not 
insignificant amount of their matter in the form of cool gas 
clouds. Several astronomers now believe the Local Group, and 
other clusters, to be threaded with ribbons and streamers of 
gas. 

But what do these clouds represent? Many are as big as 
150,000 light-years across and contain a mass equivalent to 
hundreds of millions of stars. Might they be about to form into 
irregular galaxies? This is the tempting suggestion proffered by 
a few theorists; but other calculations indicate that the clouds 
are unstable, and will tend to expand, rather than contract to 
form stars. A great deal of work clearly remains to be done 
before their true nature becomes known; but it is gratifying 
that this new knowledge was triggered by discoveries made 
within our Local Group. 



194 



WHAT'S NEW IN THE LOCAL GROUP? 

Is there anything left to discover? 

We have, by now, surveyed the Local Group fairly thor- 
oughly. Surely, nothing remains to be discovered, except 
perhaps an occasional dwarf galaxy, tramp globular cluster, or 
small gas cloud? But we have reckoned without one very 
important fact: there are parts of our Local Group which we 
cannot easily see. The dust in the disk of our Galaxy not only 
shrouds our view of the galactic centre; it also prevents us from 
seeing clearly into space in all directions along the galactic 
plane. 

Although our eyes and optical telescopes cannot penetrate 
the fog, long infrared wavelengths can. An astronomer called 
Maffei made a special search of the galactic plane at these 
wavelengths in 1968, and was rewarded by the discovery of two 
highly obscured objects lying close to each other only half a 
degree from the plane. But they were amorphous, fuzzy 
patches which could just as easily have been globular clusters 
as galaxies. So followed an ambitious research programme — 
using the world's finest instruments — to establish their true 
identity. 

Both objects — Maffei I and Maffei II — proved to be galax- 
ies. More excitingly, Maffei I was shown to lie only three 
million light-years away — well within the Local Group. But 
most astonishing of all was the discovery that Maffei I is almost 
certainly a giant elliptical galaxy; the sort which populates the 
huge clusters of galaxies, and not little backwaters like our 
Local Group. Because of the tremendous obscuration in our 
own Galaxy — less than one-hundredth of Maffei I's light gets 
through to us — it is difficult to estimate just how big it is; but 
astronomers think it could well be as massive as the Galaxy, or 
even Andromeda. 

If these findings are correct, it is a staggering discovery — 
perhaps the biggest galaxy in the Local Group, hidden from 
our sight by a thick band of dust in our own Galaxy. Yet Maffei 
I's claim to membership of the Local Group does raise a few 
problems. Its kinetic energy — due to its large measured veloc- 
ity and its huge mass — is enormously greater than that of any 
other member, which raises severe doubts as to whether the 

195 



1978 YEARBOOK OF ASTRONOMY 

Local Group is stable. But rather than admit the Local Group 
is flying apart, astronomers prefer to believe that Maffei I is a 
stray galaxy just 'passing through' — and not a permanent 
resident. 

What about Maffei II? It lies only three-quarters of a degree 
from Maffei I, and has a very similar velocity; yet it has been 
shown to be a spiral galaxy, well outside the Local Group at a 
distance of some 15 million light-years. This may put it among 
the members of the Ursa Major-Camelopardus cloud of 
galaxies. But some astronomers are uneasy; they feel that the 
coincidence of position and velocity between Maffei I and II 
shows that they must be somehow related. Maffei II is almost 
certainly at the greater distance; yet there are strong reasons for 
believing that Maffei I cannot be as far away as that. Which is 
the right answer? Are both — or neither — within the Local 
Group? 

The same questions seemed destined to be asked again, 
following on from a very recent discovery by astronomers at 
Heidelberg, Germany. Searching a highly obscured region of 
the galactic plane, near the North America Nebula in Cygnus, 
they found two indistinct objects, one uncannily resembling 
Maffei I in both apparent size and light distribution. Another 
giant member of the Local Group? Was our little cluster 
greater in stature than we had hitherto believed? It was clearly 
important to find out. 

Astronomers were quick off the mark to follow up the 
Heidelberg discoveries, and both objects have now been 
examined with the Hale 5-metre telescope. One is a spiral 
galaxy similar to our own; the other a bright elliptical. It seems 
from their apparent brightness that both lie well beyond the 
boundaries of the Local Group — perhaps as far as 30 million 
light-years away. But this is still close on an extragalactic scale, 
and their discovery will add much to our knowledge of nearby 
galaxies. 

It is encouraging — even if slightly disquieting — that dis- 
coveries continue to be made on our doorstep, amidst familiar 
territory we believed we understood. So much obviously 
remains to be learned about normal galaxies, before we can 

196 



WHAPS NEW IN THE LOCAL GROUP 

tackle the more exotic problems of extragalactic astrophysics 
with confidence. But we have a head start; if we probe 
diligently enough, our Local Group will provide some of the 
answers. 



197 



Interstellar and Intergalactic Matter 



IAIN NICOLSON 

Ten years ago I wrote an article for the 1968 Yearbook on the 
subject of 'Interstellar Dust', the tiny solid grains which are 
responsible for obscuring our view of the galactic centre. 
Although in the past decade there has not been a great change 
in our view of the nature of the grains, our knowledge of the 
interstellar and intergalactic medium in general has grown out 
of all recognition. Ten years ago we had no idea that a wide 
variety of complex molecules exist in gas clouds, and the 
notion that matter might exist in the space between the galaxies 
was regarded as being highly speculative — certainly, there was 
no good evidence to support such a suggestion. Today, the 
evidence for intergalactic material is strong and the debate is 
concerned with how much material exists in this form. 

These dramatic advances in our knowledge owe much to 
developments in techniques and instrumentation, both in 
ground-based and space-borne astronomy. Advances in opti- 
cal and radio astronomy, and the development of infrared 
astronomy have allowed Earth-based observers to gain a more 
comprehensive set of observations, while satellites — orbiting 
above the masking effects of the atmosphere — have provided 
vital observations, particularly in the X-ray and ultra-violet 
regions of the spectrum. Such short-wavelength radiation is 
prevented from reaching the Earth's surface (which is good for 
us, but a nuisance for the astronomer!) by absorption in the 
upper atmosphere, and X-ray astronomy in particular can only 
be carried out by means of rockets or satellites; the first rocket 
experiment was carried out in 1962, and the first satellite 
devoted to X-ray astronomy (the U.S. Explorer satellite 

198 



INTERSTELLAR AND INTERGALACTIC MATTER 

UHURU) was launched in 1970. High altitude balloons, too, 
have made a contribution by carrying instrumentation sensi- 
tive to long-wave infra-red and short-wave microwave radia- 
tion. 

In what follows I hope to be able to give an overall impres- 
sion of our present knowledge of interstellar and intergalactic 
matter and to highlight some of the problems and uncertain- 
ties. 

Interstellar Matter 

Matter between the stars exists in two basic forms, gas (ions, 
atoms, and molecules) and dust (small solid particles, or 
grains) and the generally accepted view is that the gas makes up 
about 10 per cent of the mass of our Galaxy while the dust 
comprises only 1 per cent of the interstellar material, i.e. 0. 1 per 
cent of the galactic mass. 

The most obvious evidence for the gas is the existence of 
luminous nebulae, such as the well-known Orion Nebula 
(M42), which are gas clouds shining by absorbing ultra-violet 
radiation from hot stars embedded within them, a re-emitting 
visible light. These luminous emission nebulae are also known 
as HII regions because they are largely composed of ionized 
hydrogen. Evidence for gas spread more generally through the 
galaxy comes from interstellar lines, dark lines superimposed 
on the spectra of stars due to absorption of starlight at 
particular wavelengths as that light passes through the inter- 
stellar gas en route from the stars to the Earth. Further vital 
evidence comes from the 21 -cm radiation emitted by neutral 
(un-ionized) hydrogen. That hydrogen would emit radiation of 
that wavelength (corresponding to a frequency of 1,420 MHz) 
was predicted by H. C. van de Hulst in 1945 and this radiation 
was first detected by radio astronomers in 1951. Because such 
radiation is not affected by interstellar dust (unlike visible 
light, which is absorbed) it has proved possible to study the 
distribution of neutral hydrogen (HI regions) through virtually 
the entire extent of our Galaxy, and in this way the spiral 
structure of the system has been dramatically revealed. 

The presence of the dust is revealed in a number of ways. 

199 



1978 YEARBOOK OF ASTRONOMY 

Dark nebulae, such as the famous 'Horse-Head' nebula in 
Orion or the 'Coal Sack' in the southern Milky Way, testify to 
the obscuring effect of relatively dense dust clouds. Such 
clouds consist of a mixture of gas and dust, but whereas the gas 
does not appreciably attenuate starlight, the dust obscures the 
light from stars lying beyond. Reflection nebulae provide 
further evidence for dust; for example, long exposure photo- 
graphs of the brighter stars in the Pleiades cluster show them to 
be surrounded by faint nebulosity due to the reflection of light 
from dust particles in the vicinity of these stars. The spectrum 
of light from a reflection nebula is almost exactly the same as 
that from the central star (the starlight being reflected by the 
dust) and quite unlike the bright emission line spectrum 
characteristic of HII regions; HII regions are made to shine 
only by the hottest and most luminous types of star (stars of 
spectral type O). 

Evidence for dust spread throughout the plane of our 
Galaxy comes from the phenomena of interstellar reddening 
and extinction, and from interstellar polarization, and it is 
from observations of these phenomena that our understanding 
of interstellar grains has come. By comparing distant stars with 
nearby stars of the same type we find that stars near the plane 
of our Galaxy appear both fainter and more red in colour than 
we would expect. Light from distant stars is scattered by the 
intervening dust particles with the result that a certain propor- 
tion is absorbed in space, the amount of extinction— on aver- 
age—amounting to one stellar magnitude per kiloparsec; this 
means that a star at a distance of one kiloparsec (3,260 light 
years) will appear to be only about two-fifths of the brightness 
we would expect it to have at such a distance. The amount of 
extinction which occurs depends on the wavelength of light, 
and over the optical region of the spectrum, the extinction is 
more or less inversely proportional to wavelength, i.e. the 
amount of extinction increases v/ith decreasing wavelength. As 
a result, blue light is more strongly absorbed than red light, and 
the proportion of red light compared to blue light which we 
receive from a star is greater than the proportion of red to 
blue light emitted by the star; in other words, the star appears 

200 



INTERSTELLAR AND INTERGALACTIC MATTER 

redder than it ought to do. This is the phenomenon of interstel- 
lar reddening. 




'\{ units of /fin" 1 ) 



Figure 1. Interstellar extinction: The amount of extinction (^m), expressed in 
stellar magnitudes is plotted against 1/A. where \ is the wavelength of radiation 
expressed in terms of the number of waves per micrometre (thus the figure 2 on the 
horizontal scale corresponds to two waves per micrometre (jim), i.e. a wavelength 
of 0.5 micrometres) 



In recent years, observations of interstellar extinction have 
been made in the infra-red and ultra-violet parts of the 
spectrum as well as the optical region and the resulting 
extinction curve is illustrated in Figure 1 , where the amount of 
light absorbed ( Am, measured in magnitudes) is plotted 
against 1/A, where A denotes the wavelength of radiation. In 

201 



1978 YEARBOOK OF ASTRONOMY 

the near infra-red the amount of extinction is small and varied 
considerably from place to place in the Galaxy. At optical 
wavelengths, the amount of extinction is inversely propor- 
tional to wavelength, but a curious feature is the pronounced 
change in slope which occurs at a wavelength of about 430 
nanometres (4,300 Angstroms, in old-fashioned units). The 
amount of extinction increases at ultra-violet wavelengths and, 
although there are differences in different parts of the Galaxy, 
the most striking feature is the 'hump' at 1/ X =4.6 (i.e. a 
wavelength of 220 nanometres). 

The general features of the extinction curve suggest that the 
particles responsible must be small, ranging in radius from 10~ 8 
to 10~ 6 metres (i.e. from a hundred millionth to a millionth of a 
metre) so that the average grain is smaller than the wavelength 
of visible light. The infra-red observations are complicated in 
some cases by that fact that there are stars which have 
circumstellar dust shells — these shells absorb radiation from 
the central stars, re-emitting it in the infra-red part of the 
spectrum (the infra-red properties of dust clouds and circum- 
stellar shells have been covered in previous Yearbook articles, 
e.g. by D. A. Allen, 'The Dusty Sky', and M. Cohen, 'Ice in 
Space', both in the 1977 edition). Many models of grains have 
been proposed to try to account for the extinction curve, but as 
yet no single model has proved to be satisfactory. The most 
popular models suggest that the grains may be composed of 
silicates, or graphite (a form of carbon), but other possibilities 
include iron and ice, and core-mantle grains (a graphite core, 
coated with, for example, water ice). Graphite grains could 
account for the ultra-violet 'hump' since graphite absorbs 
strongly at about this wavelength, but it would seem that very 
small particles would be required. Silicate grains could account 
for strong absorption observed at certain infra-red wave- 
lengths in the spectra of highly reddened stars. Ice also 
produces absorption at infra-red wavelengths, and in the past 
few years such features have been observed. 

The situation is rather confused and the best hope at present 
is that some mixture of grains of differing composition and 
sizes will fit the observations. 

202 



INTERSTELLAR AND INTERGALACTIC MATTER 

Measurements of polarization* reveal that the grains are not 
spherical, but elongated. If the long axes of the grains can be 
aligned in some way — for example by the galactic magnetic 
field— then they will preferentially absorb light vibrating in one 
particular plane, so giving rise to polarized starlight. Thus, it 
seems in the light of present evidence, that interstellar dust is 
made up of elongated grains, possibly of graphite, ice or 
silicates, comparable with or smaller than the wavelength of 
visible light. 

The origin of the grains remains something of a problem. It 
is generally agreed that formation of graphite grains may take 
place in the atmospheres of cool carbon-rich stars, and that 
after their formation, the grains are driven out from these stars 
by the pressure of radiation. Thus, we can visualize carbon 
stars leaving a trail of 'smoke' in their wake! A similar process 
could lead to the formation of silicate grains in oxygen-rich 
stars. A basic problem is that current estimates suggest that 
only a tenth of the supposed quantity of grains could be 
produced in this way. It may be that grain formation takes 
place in circumstellar shells, too, or that larger grains grow in 
interstellar space on the smaller grains expelled from stars. For 
the moment, however, it is not at all clear where all the grains 
have come from. And there is a 'chicken and egg' problem 
too — some theories suggest that grains may be necessary to 
assist the process of star formation, but if the grains have to be 
formed in stars in the first place . . . ? 

The possibility that there may be far less dust in space than 
we have hitherto supposed has also been raised. The conven- 
tional view is that the mean density of interstellar gas is about 
10" 21 kg per cubic metre (about one thousand million million 
millionth of the density of air at ground level!) and that of the 



* Polarization: A light wave vibrates in a plane perpendicular to its direction of 
motion. An unpolarized beam of light contains waves vibrating in every plane 
while a plane polarized beam contains waves vibrating in one plane only. Light 
may be in any state of polarization between these two extremes, and analysis of 
polarization can tell us a great deal about the origin of the light, or what has 
happened to it between leaving its source and reaching the Earth. 

203 



1978 YEARBOOK OF ASTRONOMY 

dust about 10" 23 kg per cubic metre. Satellite observations 
appear to indicate that some of the heavy elements (such as 
silicon) expected to be contained ingrains are in shorter supply 
in interstellar space than was previously thought. Further- 
more, Wesson and Lerman have argued that spinning dust 
grains ought to emit microwave radiation, and the fact that this 
radiation has not yet been detected implies that the mean space 
density of dust grains may be less than one-thousandth of the 
conventional value. If these arguments are confirmed then it 
may be that our view of the quantity and/ or composition of 
interstellar grains will have to be revised. 

Whatever the mean density of dust may be, the dark dense 
gas and the dust clouds which we know to exist provide the 
ideal setting for the formation of complex molecules. Until 
comparatively recently it had been thought that conditions in 
space were wholly inimical to the formation of molecules, but 
in 1963 came the discovery of one of the simplest, hydroxyl 
(OH), a combination of oxygen and hydrogen. In the past 
decade, the number of molecular species detected has exceeded 
three dozen; although some of the simpler species such as OH 
and H 2 (molecular hydrogen) reveal themselves by their 
absorption of visible or ultra-violet light, all other molecules 
have been detected by their absorption or emission of radiation 
at microwave and radio wavelengths. 

Molecules rotate and vibrate; changes in the rotational 
states accompany absorption and emission at microwave 
frequencies, while infra-red molecular spectra result from 
changes in the vibrational states. Some of the molecular species 
emit radiation by acting as masers. The molecules which have 
been found are predominantly organic, and examples include 
formaldehyde (H 2 CO), formic acid (HCOOH), and ethyl 
alcohol (C 2 H 5 OH). A particularly interesting cloud, rich in 
molecules (and containing practically all the types of molecule 
so far discovered) is Sagittarius B2 (SgrB2), a massive cloud, 
containing several million solar masses of material, lying close 
to the galactic centre. Within this cloud alone it has been 
estimated that there is sufficient ethyl alcohol to make up 10 28 
measures of proof spirit— more than enough to fill the entire 

204 



INTERSTELLAR AND INTERGALACTIC MATTER 

Earth with alcohol! What an incentive to develop interstellar 
travel! 

Intergalactic matter 

Clearly the interstellar medium is a fascinating laboratory 
offering tremendous scope for observational and theoretical 
work, and many problems remain to be solved. What do we 
know of the space between the galaxies? 

We can certainly rule out the possibility that there exists 
large quantities of intergalactic dust similar to interstellar 
grains. Intergalactic space is very transparent; we can see 
galaxies at ranges of over 10 10 (ten thousand million) light 
years and this implies that the mean density of dust must be less 
than a few times 10" 30 kg per cubic metre. If we were to assume 
that the proportion of gas to dust in intergalactic space were 
the same as that found in the Galaxy then we would expect to 
find less than a few times 10* 28 kg per cubic metre of gas 
between the galaxies. However, since we believe that the heavy 
dust particles are produced in the more recent generations of 
stars in galaxies, and that the Universe originated a finite time 
ago, it is likely that the proportion of dust in intergalactic space 
will be very much less than that found in the Galaxy. A lack of 
intergalactic dust, therefore, does not necessarily imply that 
there must be very little intergalactic gas. 

The amount of intergalactic matter (gas, dust, or whatever) 
is of profound cosmological importance. The evidence at 
present favours the 'Big-Bang' origin of the Universe, i.e. that 
the Universe 'began' in a hot explosive event nearly twenty 
thousand million years ago. At present the Universe is expand- 
ing but, due to the mutual gravitational attraction of matter, 
the expansion is slowing down. Either the expansion will slow 
down to a steady level and continue without limit, or, if the 
mean density of matter in the Universe exceeds a certain value 
(the critical density), the expansion will eventually halt, to be 
followed by a contraction phase. Estimates of the mean density 
based on the observed number of galaxies fall far below the 
critical density (which is about 5 X 10~ 27 kg per cubic metre), by 
a factor of between ten and a hundred, but if large amounts of 

205 



1978 YEARBOOK OF ASTRONOMY 

intergalactic and invisible matter exist, then there may be 
sufficient mass eventually to halt the expansion. 

Evidence for intergalactic matter has built up in the past 
decade from widely different types of observations. Firstly, 
there is the question of the 'missing mass' in clusters of galaxies. 
The galaxies which make up a cluster all have their individual 
motions and so possess kinetic energy; in order that the 
members be held together the cluster must contain sufficient 
mass such that the gravitational attraction exerted on each 
galaxy prevents its escaping from the group. There is a theorem, 
known as the virial theorem, which relates the kinetic energy of 
galaxies in a cluster to the gravitational potential energy of the 
cluster, and by observing the distribution and motions of 
galaxies within a cluster it is possible to deduce the expected 
mass of the cluster. In many cases the mass deduced from 
counting the number of galaxies is far less than the virial mass 
of a cluster and it follows that there must be a large amount of 
unseen 'missing' matter in such clusters. An example is the 
Coma cluster, some 450 million light years distant, which 
contains about a thousand galaxies, the combined mass of 
which has been estimated at 6 X 10 14 solar masses. However, 
the virial theorem tells us the mass of the cluster should be 
about ten times greater than this. Where is the missing mass? Is 
it contained in very faint galaxies which cannot be seen, in the 
outer parts of galaxies which do not show up in photographs, 
in massive black holes, or is it contained in intergalactic gas 
within the cluster? 

Radio astronomy provides another clue. A typical radio 
galaxy consists of two radio-emitting regions (probably clouds 
of electrons) stretching out on either side of a central optical 
galaxy. In some cases, the shape of the radio sources (which 
appear to have 'tails') suggests that the radio-emitting material 
is moving through a resisting medium of intergalactic gas. For 
example, the radio tails observed in the Perseus cluster could 
be explained by the existence of intergalactic gas within the 
cluster having a density a thousand times greater than the 
critical density. 

The most striking recent evidence has come from X-ray 

206 



INTERSTELLAR AND INTERGALACTIC MATTER 

observations. No less than twenty of the X-ray sources catalo- 
gued by the UHURU satellite turned out to be clusters of 
galaxies. Of the possible mechanisms for producing X-rays, the 
most reasonable at present is to assume that the radiation 
comes from a hot intergalactic gas (with temperatures of a few 
hundred million degrees Kelvin) in these clusters. Quite good 
agreement between observation and theory has been obtained 
in the cases of the Perseus and Coma clusters. For example, the 
Coma X-ray results could be explained by a hot gas having a 
total mass about 5 X 10 14 solar masses, i.e. about the same 
amount of mass exists in the form of hot gas as is tied up in the 
galaxies in this particular cluster. Even if this is so, however, 
the combined mass of galaxies and gas is still less than a quarter 
of the virial mass — the problem of missing mass in the Coma 
cluster remains. 

Recent observations by Gull and Northover of Cambridge 
appear to provide further support for the existence of hot gas in 
clusters. The cosmic microwave radiation (which appears to be 
radiation filling space and dating from the 'Big Bang') should 
interact with electrons in the hot gas within clusters to produce 
a small diminution of the observed 'temperature' of this 
radiation compared to the general background. Their observa- 
tions of a number of clusters (including the Coma cluster), 
although tentative, do appear to show the effect. 

Taking all the evidence into account, it does begin to look as 
if, within clusters, there may be a tenuous gas (a few hundred 
atoms per cubic metre) at a temperature of a few hundred 
million degrees absolute. It is as yet uncertain where this gas 
came from; possibly it may have been expelled from the 
member galaxies in the past, or it may have fallen into the 
clusters from inter-cluster space. Whatever its origin, it looks 
at present as if intergalactic gas cannot — of itself— wholly 
account for the 'missing mass' in clusters. 

Evidence for gas between clusters is much more tenuous. 
Attempts to detect inter-cluster neutral hydrogen or low- 
temperature ionized gas have not met with success, but it is still 
possible that a hot rarefied gas may exist. G. B. Field has 
suggested that the diffuse background X-ray radiation which 



207 



1978 YEARBOOK OF ASTRONOMY 

has been observed could be acounted for by a hot gas in 
intercluster space, having a temperature of hundreds of milli- 
ons of degrees Kelvin, but a density appreciably less than one- 
tenth of the critical density. At present, though, it is too early to 
make definite pronouncements about gas between clusters of 
galaxies. 

There is a cosmological argument whichargues against very 
large amounts of intergalactic matter. It is assumed (accepting 
the 'Big Bang' model) that most of the helium in the Universe 
was formed at the high temperature which prevailed in the first 
few minutes after the 'Big Bang'. Likewise, the observed cosmic 
abundance of the element deuterium ('heavy' hydrogen) can 
best be explained by assuming it was formed in the 'Big Bang'. 
The amount of deuterium formed depends strongly on the 
initial temperature and density of the Universe and to account 
for the observed quantities of deuterium we require that the 
mean density of matter in the Universe be no more than 10 or 
20 per cent of the critical density. It is possible that the mean 
density of matter is greater than this, but if so, some other 
explanation of the origin of deuterium will be required. 

Taking all the strands of evidence together, it appears pretty 
certain that intergalactic matter exists, but that its mean 
density is probably less than one-tenth of the critical density. 
There does not seem to be sufficient matter to 'close' the 
Universe and it looks as if the expansion must continue for 
ever. However, there is still sufficient uncertainty to make us 
very wary of making such a dogmatic statement, and it may be 
that the intergalactic medium has many surprises in store for us 
in the years ahead. 

Summary 

Interstellar space in our Galaxy is filled with a tenuous 
mixture of gas (predominantly hydrogen and helium), and 
dust, the mean overall density of which is about 10 21 kg per 
cubic metre. The dust is thought to comprise about 1 per cent 
by mass of the interstellar matter, but there is some evidence to 
suggest its contribution may be much less. Intergalactic matter 
appears to exist in clusters of galaxies in the form of hot gas 

208 



INTERSTELLAR AND INTERGALACTIC MATTER 

having a mean density of 10 24 kg per cubic metre in the case of 
clusters which are X-ray sources. Hot gas may exist between 
clusters of galaxies but the evidence as yet is rather uncertain, 
and there does not seem to be nearly enough matter to halt the 
headlong expansion of the Universe. Our picture of space has 
changed dramatically from the vision of stark emptiness of the 
last century to the concept of a Universe filled with a tenuous 
but complex mixture of matter and radiation, and the study of 
the interstellar and intergalactic medium has been shown to 
have profound implications for most aspects of astronomy, 
from the formation of stars and planets to the origin and 
evolution of the Universe itself. 



209 



Recent Advances in Astronomy 



PATRICK MOORE 

It is seldom nowadays that a year passes without several spec- 
tacular new developments in astronomy and space research, 
but the months which have elapsed since I wrote my last 
'Recent Advances' article, in the 1977 Yearbook, have been 
more fruitful than most. I must again stress that I am writing at 
the end of June, 1977. Who knows what else may have 
happened before my article appears in print. 

Let us begin with the Solar System— and, frankly, some- 
thing of an anti-climax. I think everyone had hoped that the 
Viking missions would give a final answer to the age-old 
question: "Is there life on Mars?" Regrettably, they have not. 
No definite signs of life have been detected; it is too early to say 
that Mars is sterile, but the Viking search for life is over, and 
the biology instruments in both Landers were switched off at 
the end of May 1977. Moreover, Viking 2 has been 'closed 
down' to prepare for the Martian winter; Utopia is a cold 
place— colder than Chryse, the site of Lander 1, since it is 
closer to the pole. Most of the other experiments are still in 
working order, and both Landers may well have a reasonable 
'active time' ahead of them— apart from the biology. 

Pioneer II continues its journey toward a rendezvous with 
Saturn, and two more deep-space probes, Voyagers 1 and 2, 
are due to be launched in the late summer. (Both should be en 
route for Jupiter, the first rendezvous, before this Yearbook 
appears in print, though one must never be over-confident; 
remember Mariners 1 and 3!). But the main discovery of 1977 
with regard to the outer planets has concerned Uranus, which 
has yielded up a long-kept secret. 

210 



UECENT ADVANCES IN ASTRONOMY 

On 10 March 1977 Uranus occulted a 9th-magnitude star, 
SAO 158687. Predictions were made by Gordon Taylor, of the 
Royal Greenwich Observatory, who has specialized in this 
kind of work, his main aim being to improve our knowledge of 
the diameters of objects which are difficult to measure 
directly.* Observations were made from the Kuiper Airborne 
Observatory, with its 36-inch reflector, and from South Africa. 
The results were totally unexpected. Before occultation, and 
again afterwards, the star 'winked' five times, and there can be 
only one explanation: Uranus is surrounded by a system of five 
rings which are so dim that they remain undetected (and are 
probably undetectable visually) from Earth. From the current 
data, it seems that the rings are contained in a narrow belt 
about 4,400 miles wide, lying 1 1,000 miles above the cloud-tops 
of Uranus itself. The first four are thought to be about 6 miles 
across, and to be almost circular. The outermost ring may be 
thicker— perhaps up to 60 miles— and may not be exactly 
circular. 

Another discovery, made independently, is that both Uranus 
and Neptune are slower spinners than has been thought. The 
axial rotation period of Uranus is now thought to be between 
17 and 22 hours; for Neptune, about 23 hours. Clearly there is 
much that we do not know about these remote giants, and 
astronomers eagerly await the moment in the year 1986 when it 
is hoped that Voyager 1 will by-pass Uranus and send us back 
information from close range. 

Still in the Solar System: much has been heard of the 
comparative lack of activity in the Sun during recent years. The 
last maximum took place in 1969, so that the next should be 
due in 1980; but sunspots were rare in 1976 and the first half of 
1977, and there were even suggestions that we were about to 
experience another 'Maunder Minimum' (the period between 
'1645 and 1715, when there were practically no spots at all and 
even the corona may have been absent, so that the solar cycle 

*I am delighted to say that the 1979 Yearbook will contain two articles about Uranus- 
one by Gordon Taylor, whose predictions led directly to the discovery of the rings, and 
one by Dr. Garry Hunt, dealing with the make-up of this peculiar world. 

211 



1978 YEARBOOK OF ASTRONOMY 

was temporarily suspended). However, this appears most 
improbable, and it is overwhelmingly likely that activity will 
pick up rapidly from now on, though it is still not certain how 
energetic the next maximum will be. 

Turning to the universe as a whole, there has been a 
fascinating discovery of a flat, disk-shaped, highly luminous 
stellar object: M WC 349, in Cygnus, which is a star surrounded 
by a disk of intensely glowing gas which may indicate that a 
planetary system is in the process of formation. The star itself is 
10 times the size and 30 times the mass of the Sun; it is 10,000 
light-years away, and is thought to be no more than a thousand 
years old. The total brightness of the object (star plus disk) is 
declining at about one per cent per month as luminous material 
from the disk spirals into the central star, so that the disk itself 
will cease to shine by AD 2077. The discovery was made by a 
team of astrophysicists headed by Dr. R. Thompson of the 
Steward Observatory, University of Arizona. It was 
announced only in June 1977, so that the data are far from 
complete as yet, but MWC349 is evidently an object of 
tremendous significance. 

Next comes the second visual identification of a pulsar. 
Pulsars— neutron stars — are detected by means of their 
rapidly-varying radio waves, but before 1977 the only pulsar 
which had been identified with a flashing object was that in the 
Crab Nebula. (It is amazing how often the Crab crops up in 
modern astronomy!) It was, however, thought that there might 
be a possibility of tracking down light from another pulsar, 
PSR 0833-45 in the southern constellation of Vela, which had 
been discovered in 1968 at the Molongo Radio Astronomy 
Observatory in Australia. The Vela pulsar has a period of 0.089 
second, the third shortest known (the shortest of all is the Crab 
pulsar, with 0.033 second), indicating that it is young, with an 
age of less than 10,000 years. Fairly obviously it is a supernova 
remnant, and it is associated with an extended area of optical 
nebulosity and radio emission. 

At Siding Spring, in Australia, a team of researchers includ- 
ing Professor Graham Smith, Director of the Royal Greenwich 
Observatory, and Dr. Paul Murdin, also from Greenwich, 

212 



RECENT ADVANCES IN ASTRONOMY 

carried out a careful search — and were successful. The Vela 
pulsar was identified with an excessively faint object which had 
been discovered in 1975 by B.M. Lasker at the Cerro Tololo 
Observatory in Chile. The visual magnitude is of approximate 
magnitude 25, which means that it is the faintest object ever 
recorded — yet another record. It is much dimmer than the 
Crab pulsar, which has a visual magnitude of 17. The Siding 
Spring triumph gives hope that in the foreseeable future other 
pulsars may be optically identified, though the task is an 
extremely difficult one. It is, incidentally, notable that we now 
know more about pulsars than we do about quasars, which 
were discovered considerably earlier but which remain very 
enigmatical indeed. 

New telescopes continue to be built (one of the latest is an 84- 
inch in Argentina, several hundred miles west of Buenos 
Aires), though the Russian 236-inch remains supreme in point 
of size; whether it will ever be surpassed by an Earth-based 
instrument remains to be seen. So far as England is concerned, 
the largest telescope has been the 98-inch at Herstmonceux; it 
is far greater in aperture than any other British telescope — 
indeed, its nearest rival has been the remarkable 72-inch built 
by the third Earl of Rosse as long ago as 1845, but which has 
now been out of use for more than sixty years. Unfortunately, 
it has to be admitted that the English climate is not ideal 
astronomically, and the 98-inch cannot often be used to its full 
capacity. For some time there have been plans to transfer it to a 
better site, and it has now been decided that the new Northern 
Hemisphere Observatory (NHO for short) will be set up at La 
Palma, in the Canary Islands. The 98-inch telescope is to be 
transferred there, equipped with a new mirror which will 
actually be a full 100 inches across and, of course, with a highly 
modified mount to allow for the difference in latitude. In a way 
it is a pity that Herstmonceux should lose its largest telescope, 
but clearly the decision has been in the best interests of science. 
It is worth adding, incidentally, that a major public exhibition 
has now been opened at Herstmonceux, and is proving 
extremely popular with the many visitors who go there. 

On the debit side, we have lost one of our greatest astronom- 

213 



1978 YEARBOOK OF ASTRONOMY 

ers: Dr. Donald H. Menzel, who was eminent in so many fields 
and was particularly renowned for his work in connection with 
the Sun. Dr. Menzel's death was sudden and unexpected; he 
will be sadly missed, not only for his scientific eminence but 
also for his outstanding personal qualities. I knew him well, 
and so can speak with authority. 

What lies ahead? Progress is now amazingly rapid in both 
space research and what may be termed 'old-fashioned astron- 
omy'. Photography itself is giving way to electronic methods; 
in America, the Space Shuttle is being prepared; artificial 
satellites are providing striking new information about topics 
such as X-ray astronomy, and it must be added that a large new 
English infra-red telescope is being erected in Hawaii. Astron- 
omy now is very different from that of 1962, when the first 
Yearbook was published. Exciting times lie ahead. 



214 



PART THREE 

Miscellaneous 



Some Interesting Telescopic 
Variable Stars 



Star 


R.A. 


Dec. 




h 


m 


° 




R. Andromeda; 





22 


+38 


18 


W Andromeda 


2 


14 


+44 


4 


Theta Apodis 


14 


00 


-76 


33 


R Aquila; 


19 


4 


+ 8 


9 


R Arietis 


2 


13 


+24 


50 


R Arae 


16 


35 


-56 


54 


R Auriga; 


5 


13 


+53 


32 


R Bobtis 


14 


35 


+26 


57 


Eta Carinae 


10 


43 


-59 


25 


I Carina; 


09 


43 


-62 


34 


R Cassiopeia; 


23 


56 


+51 


6 


T Cassiopeia; 





20 


+55 


31 


X Centauri 


11 


46 


-41 


28 


T Centauri 


13 


38 


-33 


21 


T Cephei 


21 


9 


+68 


17 


R Crucis 


12 


20 


-61 


21 


Omicron Ceti 


2 


17 


- 3 


12 


R Corona; Borealis 


15 


46 


+28 


18 


W Corona; Borealis 


16 


16 


+37 


55 


R Cygni 


19 


35 


+50 


5 


U Cygni 


20 


18 


+47 


44 


W Cygni 


21 


34 


+45 


9 


SS Cygni 


21 


41 


+43 


21 


Chi Cygni 


19 


49 


+32 


47 


Beta Doradfls 


05 


33 


-62 


31 


R Draconis 


16 


32 


+66 


52 


R Geminorum 


7 


4 


+22 


47 


U Geminorum 


7 


52 


+22 


8 


R Gruis 


21 


45 


-47 


09 


S Gruis 


22 


23 


-48 


41 


S Herculis 


16 


50 


+ 15 


2 


U Herculis 


16 


23 


+ 19 





R Hydra; 


13 


27 


-23 


1 


R Leonis 


9 


45 


+ 11 


40 


X Leonis 


9 


48 


+12 


7 


R Leporis 


4 


57 


-14 


53 


R Lyncis 


6 


57 


+55 


24 


W Lyra; 


18 


13 


+36 


39 


T Norma: 


15 


40 


-54 


50 


HR Delphini 


20 


40 


+ 18 


58 


S Octantis 


17 


46 


-85 


48 


U Orionis 


5 


53 


+20 


10 


Kappa Pavonis 


18 


51 


-67 


18 


R Pegasi 


23 


4 


+ 10 


16 


S Persei 


2 


19 


+58 


22 


R Sculptoris 


01 


24 


-32 


48 





Period, 


Mag. range 


days 


Remarks 


6.1-14.9 


409 




6.7-14.5 


397 




6.4- 8.6 


119 


Semi-regular. 


5.7-12.0 


300 




7.5-13.7 


189 




5.9-6.9 


4 


Algol type. 


6.7-13.7 


459 




6.7-12.8 


223 




-0.8- 7.9 


— 


Unique erratic 
variable. 


3.9-10.0 


381 




5.5-13.0 


431 




7.3-12.4 


445 




7.0-13.9 


315 




5.5- 9.0 


91 


Semi-regular. 


5.4-11.0 


390 




6.9- 8.0 


5 


Cepheid. 


2.0-10.1 


331 


Mira. 


5.8-14.8 


- 


irregular 


7.8-14.3 


238 




6.5-14.2 


426 




6.7-11.4 


465 




5.0- 7.6 


131 




8.2-12.1 


- 


Irregular. 


3.3-14.2 


407 


Near Eta. 


4.5- 5.7 


9 


Cepheid. 


6.9-13.0 


246 




6.0-14.0 


370 




8.8-14.4 


- 


Irregular. 


7.4-14.9 


333 




6.0-15.0 


410 




7.0-13.8 


307 




7.0-13.4 


406 




4.0-10.0 


386 




5.4-10.5 


313 


Near 18, 19. 


12.0-15.1 


- 


Irregular 
(U Gem type). 


5.9-10.5 


432 


'Crimson star.' 


7.2-14.0 


379 




7.9-13.0 


196 




6.2-13.4 


293 




3.6- ? 


_ 


Nova, 1967. 


7.4-14.0 


259 




5.3-12.6 


372 




4.0- 5.5 


9 


Cepheid. 


7.1-13.8 


378 




7.9-11.1 


810 


Semi-regular. 


5.8- 7.7 


363 


Semi-regular. 



217 



1978 YEARBOOK OF ASTRONOMY 



Star 


R.A. 


Dec. 




Perioa 


F 




h 


m 


° 


' 


Mag. range 


days 


Remarks 


R Phoenicis 


23 


53 


-50 


05 


7.5-14.4 


268 




Zeta Phoenicis 


01 


06 


-55 


31 


3.6- 4.1 


1 


Algol type. 


R Pictoris 


04 


44 


-49 


20 


6.7-10.0 


171 


Semi-regular. 


L 2 Puppis 


07 


12 


-44 


33 


2.6- 6.0 


141 


Semi-regular. 


Z Puppis 


07 


30 


-20 


33 


7.2-14.6 


510 




T Pyxidis 


09 


02 


-32 


11 


7.0-14.0 


- 


Recurrent nova 
(1920, 1944) 


R Scuti 


18 


45 


- 5 


46 


5.0- 8.4 


144 




R Serpentis 


15 


48 


+ 15 


17 


5.7-14.4 


357 




SU Tauri 


5 


46 


+19 


3 


9.2-16.0 


" 


Irregular 
(R CrB type). 


R Ursa; Majoris 


10 


41 


+69 


2 


6.7-13.4 


302 




S Ursa; Majoris 


12 


42 


+61 


22 


7.4-12.3 


226 




T Ursa; Majoris 


12 


34 


+59 


46 


6.6-13.4 


257 




S Virginis 


13 


30 


-6 


56 


6.3-13.2 


380 




R Vulpeculae 


21 


2 


+23 


38 


8.1-12.6 


137 





Note: Unless otherwise stated, all these variables are of the Mira type. 

Some Interesting Double Stars 

The pairs listed below are well-known objects, and all the 
primaries are easily visible with the naked eye, so that right 
ascensions and declinations are not given. Most can be seen 
with a 3-inch refractor, and all with a 4-inch under good 
conditions, while quite a number can be separated with smaller 
telescopes, and a few (such as Alpha Capricorni) with the 
naked eye. Yet other pairs, such as Mizar-Alcor in Ursa Major 
and Theta Tauri in the Hyades, are regarded as too wide to be 
regarded as bona-fide doubles! 



Name i 


Magnitudes 


Separation" 


Position 
angle, deg. 


Remarks 


Gamma Andromeda; 


3.0,5.0 


9.8 


060 


Yellow, blue. B is again 
double (0".4) but needs 
a larger telescope. 


Zeta Aquarii 


4.4,4.6 


2.6 


291 


Becoming more difficult. 


Gamma Arietis 


4.2, 4.4 


8 


000 


Very easy. 


Theta Auriga; 


2.7, 7.2 


3 


330 


Stiff test for 3 in. OG 


Delta Bootis 


3.2, 7.4 


105 


079 


Fixed. 


Epsilon Bootis 


3.0, 6.3 


2.8 


340 


Yellow, blue. Fine pair. 


Kappa Bootis 


5.1,7.2 


13 


237 


Easy. 


Zeta Cancri 


5.6,6.1 


5.6 


082 




Iota Cancri 


4.4, 6.5 


31 


307 


Easy. Yellow, blue. 


Alpha Canum Venat. 


3.2,5.7 


20 


228 


Yellowish, bluish. Easy. 


Alpha Capricorni 


3.3,4.2 


376 


291 


Naked-eye pair. Alpha 
again double. 


Eta Cassiopeia; 


3.7,7.4 


11 


298 


Creamy, bluish. Easy. 


Beta Cephei 


3.3, 8.0 


14 


250 




Delta Cephei 


var, 7.5 


41 


192 


Very easy. 



218 



SOME INTERESTING DOUBLE STARS 



Name 


Magnitudes 


Separation 


" Position 
angle, deg. 


Remarks 


Alpha Centauri 


0.0,1.7 






Binary; period 80 years. 
Very easy. 


Xi Cephei 


4.7, 6.5 


6 


270 


Reasonably easy. 


Gamma Ceti 


3.7,6.2 


3 


300 


Not too easy. 


Alpha Circini 


3.4, 8.8 


15.8 


235 


PA, slowly decreasing. 


Zeta Coronas Borealis 


4.0, 4.9 


6.3 


304 




Delta Corvi 


3.0, 8.5 


24 


212 




Alpha Crucis 


1.6,2.1 


4.7 


114 


Third star in low- 
power field. 


Gamma Crucis 


1.6,6.7 


111 


212 


Wide optical pair. 


Beta Cygni 


3.0,5.3 


35 


055 


Yellow, green. Glorious. 


61 Cygni 


5.3,5.9 


25 


150 




Gamma Delphini 


4.0, 5.0 


10 


265 


Yellow, greenish. Easy. 


Nu Draconis 


4.6, 4.6 


62 


312 


Naked-eye pair. 


Alpha Geminorum 


2.0, 2.8 


2 


151 


Castor. Becoming easier. 


Delta Geminorum 


3.2,8.2 


6.5 


120 




Alpha Herculis 


var, 6. 1 


4.5 


110 


Red, green. 


Delta Herculis 


3.0,7.5 


11 


208 


Optical double. 


Zeta Herculis 


3.0, 6.5 


1.4 


300 


Fine, rapid binary. 


Gamma Leonis 


2.6,3.8 


4.3 


121 


Binary; period 400 years 


Alpha Lyrae 


0.0, 10.5 


60 


180 


Vega. Optical; B faint. 


Epsilon Lyras 


4.6,6.3 


3 


005 


Quadruple. Both pairs 




4.9,5.2 


2.3 


111 


separable in 3 in. OG 


Zeta Lyras 


4.2,5.5 


44 


150 


Fixed. Easy double. 


Beta Orionis 


0.1,6.7 


9.5 


205 


Rigel. Can be split with 
3 in. 


Iota Orionis 


3.2,7.3 


11 


140 


Theta Orionis 


6.0,7.0 
7.5,8.0 






The famous Trapezium in 

M.42 


Sigma Orionis 


4.0,7.0 


11.1 


236 


Quadruple. D is rather 






12.9 


085 


faint in small apertures. 


Zeta Orionis 


1.9,5.0 


3 


160 




Eta Persei 


4.0,8.5 


28.5 


300 


Yellow, bluish. 


Beta Phoenicis 


4.1,4.1 


1.3 


352 


Slow binary. 


Beta Piscis Austrini 


4.4, 7.9 


30.4 


172 


Optical pair. Fixed. 


Alpha Piscium 


4.3,5.3 


1.9 


291 




Kappa Puppis 


4.5,4.6 


9.8 


318 


Again double. 


Alpha Scorpii 


0.9, 6.8 


3 


275 


Antares, Red. green. 


Nu Scorpii 


4.2, 6.5 


42 


336 




Theta Serpentis 


4.1,4.1 


23 


103 


Very easy. 


Alpha Tauri 


0.8,11.2 


130 


032 


Aldebaran. Wide, but B 
is very faint in small 
telescopes. 


Beta Tucanae 


4.5, 4.5 


27.1 


170 


Both components again 
double. 


Zeta Ursa; Majoris 


2.3,4.2 


14.5 


150 


Mizar. Very easy. Naked 
eye pair with Alcor. 


Alpha Ursa; Minoris 


2.0,9.0 


18.3 


217 


Polaris. Can be seen with 
3 in. 
Binary; period 180 yrs. 


Gamma Virginis 


3.6, 3.7 


4.8 


305 










Closing. 


Theta Virginis 


4.0, 9.0 


7 


340 


Not too easy. 


Gamma Volantis 


3.9,5.8 


13.8 


299 


Very slow binary. 



219 



Some Interesting Nebulae and Clusters 



Object 



R.A. 



Dec. 



M.31 Andromeda? 
H.VIII 78 Cassiopeia; 


h 

00 

00 


m 

40.7 

41.3 


+41 
+61 


05 
36 


M.33 Trianguli 
H.VI 33-1 Persei 
A 142 Doradus 


01 
02 
05 


31.8 
18.3 
39.1 


+30 
+56 
-69 


28 
59 
09 


M.l Tauri 
M.42 Orionis 


05 
05 


32.3 
33.4 


+22 
-05 


00 

24 


M.35 Geminorum 
H.VH 2 Monocerotis 
M.41 Canis Majoris 
M.47 Puppis 
H.IV 64 Puppis 


06 
06 
06 

07 
07 


06.5 
30.7 
45.5 
34.3 
39.6 


+24 
+04 
-20 
-14 
-18 


21 
53 
42 
22 
05 


M.46 Puppis 
M.44 Cancri 


07 
08 


39.5 
38 


-14 
+20 


42 
07 


M.97 Ursas Majoris 
Kappa Crucis 


11 

12 


12.6 
50.7 


+55 
-60 


13 
05 


M.3 Can. Ven. 
Omega Centauri 


13 
13 


40.6 

23.7 


+28 
-47 


34 
03 


M.80 Scorpii 


16 


14.9 


-22 


53 


M.4 Scorpii 
M.13 Herculis 
M.92 Herculis 
M.6 Scorpii 
M.7 Scorpii 
M.23 Sagittarii 
H.IV 37 Draconis 
M.8 Sagittarii 


16 
16 

17 
17 
17 
17 
17 
18 


21.5 

40 

16.1 

36.8 

50.6 

54.8 

58.6 

01.4 


-26 
+36 
+43 
-32 
-34 
-19 
+66 
-24 


26 
31 
11 
11 
48 
01 
38 
23 


NGC 6572 Ophiuchi 


18 


10.9 


+06 


50 


M.17 Sagittarii 


18 


18.8 


-16 


12 


M.ll Scuti 
•M.57 Lyrae 
M.27 Vulpeculae 
H.IV 1 Aquarii 
M.15 Pegasi 
M.39 Cygni 


18 
18 
19 

21 
21 
21 


49.0 
52.6 
58.1 
02.1 
28.3 
31.0 


-06 

+32 
+22 
-11 
+ 12 
+48 


19 
59 

37 
31 
01 
17 



Remarks 



Great Galaxy, visible to naked eye. 
Fine cluster, between Gamma and Kappa 

Cassiopeiae. 
Spiral. Difficult with small apertures. 
Double cluster; Sword-handle. 
Looped nebula round 30 

Doradus. Naked-eye. In 

Large Cloud of Magellan. 
Crab Nebula, near Zeta Tauri. 
Great Nebula. Contains the famous 

Trapezium, Theta Orionis. 
Open cluster near Eta Geminorum. 
Open cluster, just visible to naked eye. 
Open cluster, just visible to naked eye. 
Mag. 5,2. Loose cluster. 
Bright planetary in rich 

neighbourhood. 
Open cluster. 
Prassepe. Open cluster near Delta Cancri. 

Visible to naked eye. 
Owl Nebula, diameter 3'. Planetary. 
"Jewel Box"; open cluster, 

with stars of contrasting 

colours. 

Bright globular. 
Finest of all globulars. 

Easy with naked eye. 
Globular, between Antares and Beta 

Scorpionis. 
Open cluster close to Antares. 
Globular. Just visible to naked eye. 
Globular. Between Iota and Eta Herculis. 
Open cluster; naked-eye. 
Very bright open cluster; naked eye. 
Open cluster nearly 50' in diameter. 

Bright Planetary. 

Lagoon Nebula. Gaseous. Just visible 
with naked eye. 

Bright planetary, between Beta Ophiuchi 

and Zeta Aquilas. 
Omega Nebula. Gaseous. Large and 
bright. 

Wild Duck. Bright open cluster. 

Ring Nebula. Brightest of planetaries. 

Dumb-bell Nebula, near Gamma Sagittas. 

Bright planetary near Nu Aquarii. 

Bright globular, near Epsilon Pegasi. 

Open cluster between Deneb and Alpha 

Lacertae. Well seen with low powers. 



220 



Some Recent Books 



Astronomy: The Structure of the Universe, by William J. 
Kaufmann. Macmillan, 1977. A very clear and 
comprehensive account of modern astronomy, suitable for 
the layman and for the serious student. 

Exploring the Galaxies, by Simon Mitton. A general account, 
very clearly written and incorporating the latest results. 

Guide to Mars, by Patrick Moore. Lutterworth Press, 1977. 
An account of Mars as it now appears following the 
successful Viking missions. 

Astronomy: a Dictionary of Space and the Universe, by Iain 
Nicolson. Arrow Books, 1977. A paperback, the title of 
which speaks for itself; invaluable as a quick reference 
book. 

Modern Astronomy. Various authors. Sidgwick & Jackson, 
1977. Reprints of articles in previous Yearbooks (1962 to 
1976), brought up to date where necessary. 



221 



Our Contributors 

F. R. S PRY is an amateur astronomer who has his observatory at 
Selsey in Sussex; the main telescope is an 8 '/ 2 in. reflector. He is 
concerned mainly with astronomical equipment, and is a regular 
contributor to the Yearbook. He is a Council Member of the 
British Astronomical Association. 



Dr R. Maddison, of Keele University, is also one of our regular 
contributors. He is in charge of the Astronomy Department at the 
university, where there is a new observatory equipped with a 
24 in. reflector. Though primarily an astrophysicist, he is also 
deeply involved with problems of the Moon. He is Vice-Presi- 
dent of the British Astronomical Association, and is a frequent 
broadcaster on both television and radio. 



J. C. D. Marsh is Senior Lecturer in Astronomy at the Hatfield 
Polytechnic. He specializes in infra-red astronomy, and has 
undertaken much original research. 



Professor S. Miyamoto, of Kwasan Observatory at Kyoto (Japan) 
has concentrated largely upon lunar and planetary research, and 
has published many papers upon the subject. He serves on the 
Lunar and Planetary Commissions of the International Astro- 
nomical Union. 

222 



OUR CONTRIBUTORS 

Dr Garry E. Hunt, of University College, London, has been 
deeply involved with the planetary probes, and has been primari- 
ly responsible for some of the experiments carried out by them. 
His main research is in connection with planetary meteorology. 
He is also well known for his broadcasts on radio and television. 



Dr Jocelyn Bell Burnell has worked in radio astronomy (where 
she was involved with the discovery of pulsars), gamma-ray 
astronomy, and is now working in X-ray astronomy at the 
Mullard Space Science Laboratory, University College, London. 
She helps run the Ariel V X-ray astronomy satellite. She is a 
Fellow of the Royal Astronomical Society, and until recently has 
been an editor of The Observatory magazine. 



Dr Simon Mitton is a Cambridge graduate, and carried out 
research on radio galaxies until 1971. He is secretary of the 
Institute of Astronomy at Cambridge, and is the U.K. editor of 
Astrophysical Letters. In addition to his technical writing he 
has recently published a more 'popular' book, Exploring the 
Galaxies. 



Heather Couper is a graduate of the University of Leicester, 
specializing in research into external galaxies. She is a Council 
Member of the British Astronomical Association. 



Iain Nicolson, a regular Yearbook contributor, is Lecturer in 
Astronomy at the Hatfield Polytechnic Observatory. He gradu- 
ated from the University of St Andrews, and has been concerned 
largely with infra-red astronomy and interstellar matter. He 
broadcasts frequently, and has served on the Council of the 
British Astronomical Association. 



223 



Astronomical Societies in Great Britain 

The advantages of joining an astronomical society are obvious 
enough. Full information about national and local Societies 
was given in the 1966 Yearbook; a condensed list, suitably 
brought up to date, is given below. 

Editor's Note. It has been decided to omit subscriptions as 
they were found to be continually out of date.) 

British Astronomical Association 

Secretary: J. L. White, Burlington House, Piccadilly, London, W.l. 

Meetings: Burlington House, Piccadilly. Last Wed. each month (Oct.-June). 
Irish Astronomical Association 

Secretary: D. Beesley, The Planetarium, Armagh. 

Meetings: Belfast, fortnightly. Armagh, monthly. 
Junior Astronomical Society 

Secretary: 58 Vaughan Gardens, Ilford, Essex. 

Meetings: Alliance Hall, Palmer Street, W.C.I. Last Saturday Jan., April, July, Oct 

2.30 p.m. 

Aberdeen and District Astronomical Society 

Secretary: W. P. Cooper, 14 Abbotshall Gardens, Cults, Aberdeen. 

Meetings: Robert-Gordon's Institute of Technology, St Andrew Street, Aberdeen. 
Altrincham and District Astronomical Society 

Secretary: Colin Henshaw, 10 Delamere Road, Gatley, Cheadle, Cheshire. 

Meetings: Park Road Library, Timperley. 1st Friday of each month, 7.30 p.m. 
Aylesbury Astronomical Society 

Secretary: N. Neale, 9 Elm Close, Butler's Cross, Aylesbury. 

Meetings: As arranged. 
Birmingham Astronomical Society 

Secretary: A. R. J. Foulger, 14 Plants Brook Road, Walmley, Sutton Coldfield. 

Meetings: Birmingham and Midland Institute. Monthly. 
Border Astronomical Society 

Secretary: David Pettit, 14 Shap Grove, Carlisle, Cumbria. 

Meetings: Morton Community Centre, Wigton Road, Carlisle. Monthly by arrange- 
ment. 
Bradford Astronomical Society 

Secretary: B. Jones, 28 High House Avenue, Bolton, Bradford, W. Yorks. 

Meetings: 
Bridgwater Astronomical Society 

Secretary: W. L. Buckland, The Bridgwater College, Bridgwater, Somerset. 

Meetings: Room 4, Blake Street Centre, Bridgwater College. 3rd Wednesday in each 

month. 
Brighton Astronomical Society 

Secretary: Mrs B. C. Smith, Flat 2, 23 Albany Villas, Hove, Sussex, BN3 2RS. 

Meetings: Preston Tennis Club, Preston Drive, Brighton. Weekly, Tuesdays. 
Bristol Astronomical Society 

Secretary: G. H. Woodman, 34 Butterfield Close, Bristol BS10 5AZ. 

Meetings: Royal Fort (Rm G44), Bristol University. Last Friday each month, Sept- 
May. 

224 



ASTRONOMICAL SOCIETIES IN GREAT BRITAIN 

Caithness and Dounreay Astronomical Society 

Secretary: Miss M. J. A. Clark, Room 31, Ormlie Lodge, Thurso, Scotland 

Meetings: Fortnightly. 
Camberley (Surrey) Astronomical Society 

Secretary: B. A. Roberts, 45 Ferndale Road, Church Crookham, Aldershot, Hants. 

Meetings: (Room B23, Yateley Centre School, School Lane, Yateley, Camberlev 

Surrey.) 2nd Wednesday each month, 7.45 p.m. 
Cambridge Astronomical Society 

Secretary: S. R. Whistler, 5 Haggis Gap, Fulbourn. 

Meetings: 7 Brooklands Avenue, Cambridge. 2nd Mon. each month Oct.-July. 
Cardiff Astronomical Society 

Secretary: D. W. S. Powell, 1 Tal-y-Bont Road, Ely, Cardiff. 

Meeting Place: Penylan Observatory, Cyncoed Road, Penylan, Cardiff. Alternate 

Thursdays, 8 p.m. 
Chelmsford and District Astronomical Society 

Secretary: Miss C. C. Puddick, 6 Walpofe Walk, Rayleigh, Essex. 

Meetings: 7.45 p.m. Sandon House School, Sandon Near Chelmsford. 2nd and 

last Monday of Month. 
Chelmsley Astronomical Society 

Secretary: Miss D. Calvert, 193 Shard End Crescent, Shard End, Birmingham. 

Meetings: Chelmsley Wood Library. Last Thursday in month. 
Chester Astronomical Society 

Secretary: A. Kemp, 37 Alwyn Gardens, Upton, Chester. 

Meetings: St Andrews House, Newgate Street, Chester. Monthly. 
Chester Society of Natural Science, Literature and Art 

Secretary: Paul Braid, 'White Wing', 38 Bryn Avenue, Old Colwyn, Colwyn Bay, 

Meetings: Grosvenor Museum, Chester. Fortnightly. 
Chesterfield Astronomical Society 

Secretary: Mrs R. C. Naylor, Hilltop Cottage, Gallery Lane, Holymoorside. Chester- 
field. 

Meetings: Barnett Observatory, Newbold. Each Friday. 
Clackmannanshire Astronomical Society 

Secretary: J. Cluckie, 9 Deer Park, Sauchie, Alloa. 

Meetings: St Mary's School, Alloa. Monthly, 3rd Friday, Sept.-May 
Clacton & District Astronomical Association 

Secretary: C. L. Haskell, 105 London Road, Clacton-on-Sea, Essex. 
Cleethorpes & District Astronomical Society 

Secretary: P. H. Rea, 236 Humberston Avenue, Humberston, Grimsby, South Hum- 

berside. 

Meetings: Beacon Hill Observatory, Cleethorpes. 1st Wednesday each month 
Clwyd Astronomical Society 

Secretary: K. J. Payne, 2 Veto Villas, Rhyl Road, Denbigh, Clwyd. 

Meetings: Details on request. 
Colchester Amateur Astronomers 

Secretary: F. Kelly, 'Middleton', Church Road, Elmstead Market, Colchester, Essex 

Meetings: William Loveless Hall, High Street, Wivenhoe. Friday evenings. Fortniehtlv 
Coventry & Warwicks Astronomical Society 

Secretary: 238 Sovereign Road, Earlsdon, Coventry, Warwicks. 

Meetings: Coventry Technical College. Fortnightly. 
Crawley Astronomical Society 

Secretary: G. Cowley, 67 Climpixy Road, Ifield, Crawley, Sussex. 

Meetings: Crawley College of Further Education. Monthly Oct.-June. 
Crayford Manor House Astronomical Society 

Secretary: R. H. Chambers, Manor House Centre, Crayford, Kent. 

Meetings: Manor House Centre, Crayford. Monthly during term-time 
Croydon Astronomical Society 

Secretary: K. Brackerborough, 342 Lower Addiscombe Road, Croydon 

Meetings: Normanton Park Hotel, 34 Normanton Road, South Croydon. Alternate 

Fridays, 7.45 p.m. 
Dartington Astronomical Society 

Secretary: Mrs Iris Allison, 'Wayfaring', Cott Lane, Dartington, Totnes, Devon. 

Meetings: Meeting Room, Shinners Bridge Centre, Dartington. 3rd Wed. each month 

at 8 p.m. Observation all other Wed. evenings (weather permitting) on Foxhole clock 
tower. 

225 



1978 YEARBOOK OF ASTRONOMY 

Derby & District Astronomical Society 

Secretary: Jane D. Kirk, 7 Cromwell Avenue, Findern, Derby. 

Meetings: At home of Secretary. First and third Friday each month, 7.30 p.m. 
Dundee Astronomical Society 

Secretary: K. Kennedy, 80 Torridon Road, Broughty Ferry, Dundee. 

Meetings: Mills Observatory, Dundee. Fortnightly in the winter. 
Eastbourne Astronomical Society 

Secretary: R. W. Cripps, 10 Framfield Way, Eastbourne. 

Meetings: Girl Guide HQ, Hartfield Road, Eastbourne. Last Saturday each month. 
East Lancashire Astronomical Society 

Secretary: D. Chadwick, 16 Worston Lane, Great Harwood, Blackburn, BB6 7TH. 

Meetings: As arranged. Monthly. 
Astronomical Society of Edinburgh 

Secretary: N. G. Matthew, 126 W. Saville Terrace, Edinburgh 9, Scotland. 

Meetings: Calton Hill Observatory, Edinburgh. Monthly. 
Ewell Astronomical Society 

Secretary: Ron W. Johnson, 19 Elm Way, Ewell, Surrey. 

Meetings: Minor Hall, Bourne Hall, Ewell. 1st Friday of each month. 
Farnham Astronomical Society 

Secretary: John Fannon, 10 Willow Way, Hale, Farnham, Surrey. 

Meetings: Adult Education Centre, 32 South Street, Farnham. 2nd Monday each 

month, 7.45 p.m. 
Fellowship of Junior Astronomers, Edinburgh 

Secretary: Miss Edith McLean, 58 Ogilvie Terrace, Edinburgh 11, Scotland. 

Meetings: Calton Hill Observatory, Edinburgh. 3rd Fri. each month, Sept- June. 
Furness Astronomical Society 

Secretary: R. Alldridge, 56 Hartington Street, Barrow-in-Furness, Cumbria. 

Meetings: Barrow Library. 1st Saturday in month, 2 p.m. 
Fylde Astronomical Society 

Secretary: 28 Belvedere Road, Thornton, Lanes. 

Meetings: Stanley Hall, Rossendale Ave. South. 1st Wed. each month. 
Astronomical Society of Glasgow 

Secretary: H. Palmer, 8 Kirkoswald Road, Newlands, Glasgow. 

Meetings: University of Strathclyde, George Street, Glasgow. 3rd Thurs. each month, 

Sept.-April. 
Great Yarmouth Astronomical Society 

Secretary: M. Poxon, 10 Tyrrels Road, Great Yarmouth, Norfolk. 

Meetings: Public Library. Alternate Fridays. 
Guildford Astronomical Society 

Secretary: Mrs D. E. Clapson, 12 Durham Close, Guildford. 

Meetings: Corona Restaurant, High Street, Guildford. 1st Tue. each month, 7.45 p.m. 
Gwynedd Astronomical Society 

Secretary: E. Parry, 2 Rhes Groes, Sling, Bangor, Gwynedd. 

Meetings: Physics Lecture Room, Bangor University. 1st Thurs. each month, 7.30 p.m. 
Astronomical Society of Haringey 

Secretary: W. T. Baker, 58 Stirling Road, Wood Green, London, N.22. 

Meetings: 673 Lordship Lane, Wood Green, London, N.22. 3rd Thurs. each month, 

7.30 p.m. 
The Hampshire Astronomical Group 

Secretary: S. W. Hackman, 52 Denbigh Drive, Fareham, Hampshire. 

Meetings: The Group Observatory. 
Harlow Astronomical Group 

Secretary: R. Marsh, 9 Charters Cross, Harlow, Essex. 

Meetings: 62 Priory Court, Harlow. Tuesdays, fortnightly, 7.30 p.m. 
Herschel Society 

Secretary: C/o Taylor Public Library, Slough. 
Hull and East Riding Astronomical Society 

Secretary: J. I. Booth, 3 Lyngarth Av., Cottingham, North Humberside. 

Meetings: College of Higher Education, Queen's Gardens, Hull. Third Friday each 

month, Oct.-April. 
Isle of Wight Astronomical Society 

Secretary: J. W. Feakins, 1 Hilltop Cottages, High Street, Freshwater, Isle of Wight. 

Meetings: Unitarian Church Hall, Newport, Isle of Wight. Monthly. 



226 



ASTRONOMICAL SOCIETIES IN GREAT BRITAIN 

Lancaster University Astronomical Society 

Secretary: G. Day, Lunar and Planetary Unit, University of Lancaster 
Meetings: 

Leeds Astronomical Society 

Secretary: M. D. Taylor, 17 Cross Lane, Wakefield, West Yorks. 
Meetings: Leeds City Museum/ Library. 2nd Wed. each month 

Leicester Astronomical Society 

Secretary: Mrs L. Withey, 26 Falmouth Road, Evington, Leicester 
Meetings: Leicester Museum and Art Gallery. Monthly. 

Lincoln Astronomical Society 

Secretary: Robert D. Christy, 41 Meadow Lake Crescent, Birchwood, Lincoln 
Meetings: The Lecture Hall, off Westcliffe Street, Lincoln. First Tues. each month 

Liverpool Astronomical Society 

Secretary: D. Bradburne, Simms Cross School House, Mitton Road, Widnes 
Meetings: City Museum, Liverpool. Monthly. 

Livingston Astronomical Society 

Secretary: 50 Dawson Avenue, Howden, Livingston, West Lothian 
Meetings: Almond Room, Howden House, Howden. Sundays, 7.30 p m 

Loughton Astronomical Society 

Secretary: S. Smith, 6 Baldock Road, Theydon Bois, Epping, Essex 
Meetings: Loughton Hall, Rectory Lane, Loughton, Essex. Thurs 8 n m 

Luton Astronomical Society 

Secretary: S. J. Anderson, 20 Bloomfield Avenue, Luton 
Meetings: Last Friday each month. 

Lytham St. Annes Astronomical Association 

Secretary: K. J. Porter, 141 Blackpool Road, Ansdell, Lytham St. Annes, Lanes 
Meetings: College of Further Education, Clifton Drive S., Lytham St. Annes. 2nd Wed 
monthly Oct.-June. 

Maidenhead Astronomical Society 

Secretary: Mr C. Wise, 592 Bath Road, Taplow, Maidenhead, Berks 
Meetings: Maidenhead Grammar School. Every 2nd Thursday. Sept.- June 

Maidenhead Astronomy Group 

Secretary: S. A. H. Roper, 129 Fane Way, Maidenhead, Berkshire. 
Meetings: Maidenhead Grammar School. Once every 3 weeks 

Manchester Astronomical Society 

Secretary: J. H. Davidson, Godlee Observatory, U.M.I.S.T., Sackville Street Man- 
chester 1. ' 
Meetings: At the Observatory, Thursdays, 7.30-9 p.m. 

Mansfield & District Astronomical Society 

Secretary: G W. Shepherd, 14 Bonnington Crescent, Sherwood Estate, Nottingham 
Meetings: Monks Precision Engineering Co., Mansfield Road, Sutton-in-Ashfield 
Last Monday of each calendar month. 

Mid-Sussex Astronomical Society 

Secretary: Dr L. K. Brundle, 63 Pasture Hill Road, Haywards Heath, Sussex 

»,-,. M S e "»g s \ Haywards Heath School, Harlands Road. Wednesdays, 7.30 p m 
Milton Keynes Astronomical Society 

tore/a^.- Paul D. Keen, 26 Betty's Close, Newton Longville, Milton Keynes, MK17 

Meetings: Alternate Tuesdays. 
Newcastle-on-Tyne Astronomical Society 

Secretary: G. E. Manville, 30 Kew Gardens, Whitley Bay, Northumberland 

Meetings: Botany Lecture Theatre, Newcastle University. Monthly, Sept -April 
Newtonian Observatory Astronomical Society 

Secretary: Miss P. E. Randle, 62 Northcott Road, Worthing, Sussex. 

Meetings: Adult Education Centre, Union Place, Worthing. 1st Wed. each month 

except Aug. 7.30. p.m. 
North Devon Astronomical Society 

Secretary: R. W. Rose, Ararat, 18 The Shields, Ilfracombe, North Devon 

Meetings: Details to be announced later. 
North Dorset Astronomical Society 

Secretary: J. E. M. Coward, The Pharmacy, Stalbridge, Dorset 

Meetings: Charterhay, Stourton, Caundle, Dorset. 2nd Wed. each month 
North Staffordshire Astronomical Society 

Secretary: E. S. Hewitt, 24 Weldon Avenue, Weston Coyney, Stoke-on-Trent. 

227 



1978 YEARBOOK OF ASTRONOMY 

Meetings: 1st Wed. of each month at Cartwright House, Broad Street, Hanley. Nosub. 

fixed yet. 
North Western Association of Variable Star Observers 

Secretary: Jeremy Bullivant, 2 Beaminster Road, Heaton Mersey, Stockport, Cheshire 

SK4 3HT. 

Meetings: Four annually. 
North Wilts/South Glos Astronomical Group 

Secretary: Simon D. Barnes, 'Kelston', Gloucester Road, Malmesbury, Wilts. 

Meetings: To be announced. 
Norwich Astronomical Society 

Secretary: Rev. Cyril D. Blount, The Manse, Back Lane, Wymondham, Norwich. 

Meetings: Norwich Observatory, Colney Lane, Cringleford, Norwich. Every Tues. and 

Sat. Public meetings 3rd Sat. at Spinney Community Centre. 
Nottingham Astronomical Society 

Secretary: C. Swift, 18 Naseby Close, Heathfield, Nottingham. 

Meetings: Monthly. , 

Orwell Astronomical Society (Ipswich) 

Secretary: M. Hadden, 33 Crofton Road, Ipswich, Suffolk. 

Meetings: Orwell Park School, Nacton, Ipswich. Weekly. 
Oxshott Astronomical Group 

Secretary: E. H. Noon, Norman Cottage, Pond Piece, Sheath Lane, Oxshott, Surrey. 

Meetings: Oxshott Village Centre. 1st Wed. each month Sept-May. 
Paisley Astronomical Society 

Secretary: Mrs J. Holms, 14 Cheviot Avenue, Barrhead, Glasgow. 

Meetings: Coats Observatory, 49 Oakshaw Street, Paisley. Monthly. 
Peterborough Astronomical Society 

Secretary: E. Pitchford, 24 Cissbury Ring, Werrington, Peterborough. 

Meetings: Peterborough Technical College. 2nd Tues., 3rd Thur. each month. 
Phoenix Astronomical Society 

Secretary: B. Jones, 38 Myers Avenue, Bolton, Bradford 2, Yorks. 

Meetings: Phoenix Park Sports Club, off Dick Lane, Thornbury, Bradford 3. 
Plymouth Astronomical Society 

Secretary: G. S. Pearce, 1 Valletort Cotts, Millbridge, Plymouth. 

Meetings: Y.W.C.A., Lockyer Street, Plymouth. Monthly. 
Portsmouth Astronomical Society 

Secretary: G. B. Bryant, 81 Ringwood Road, Southsea. 

Meetings: Monday. Fortnightly. 
Preston & District Astronomical Society 

Secretary: C. Lynch, 35 Bispham Road, Carleton, Poulton-le-Fylde, Lanes. 

Meetings: Chamber of Commerce, 49a Fishergate, Preston. 3rd Mon. each month. 

Sept. -May. 
Rayleigh Centre Amateur Astronomical Society 

Secretary: Bernard R. Soley, 136,The Chase, Rayleigh, Essex. 

Meetings: Fitzwimarc School, Hockley Road, Rayleigh. Every Wed., 8 p.m. 
Reading Astronomical Society 

Secretary: J. Wrigley, 30 Amherst Road, Reading. 

Meetings: Anderson Baptist Church Hall, Reading. Monthly. 
Salford Astronomical Society 

Secretary: J. A. Handford, 45 Burnside Avenue, Salford 6, Lanes. 

Meetings: The Observatory, Chaseley Road, Salford. 
Salisbury Plain Astronomical Society 

Secretary: R. J. D. Nias, St George's Cottage, Orcheston, Salisbury, Wilts. 

Meetings: St George's Rectory, Orcheston. Quarterly. 
Scarborough & District Astronomical Society 

Secretary: M. D. Wilson, 19 Ryefield Close, Eastfield, Scarborough, N. Yorks YOU 

3DN. 

Meetings: Osgodby Community Centre, Fortnightly, Fridays. 
Sheffield Astronomical Society 

Secretary: Mrs Nora Betts, 35 Upper Albert Road, Sheffield. 

Meetings: City Museum, Weston Bank. Third Friday each month, Sept.-May inclusive. 
Slough Astronomical Society 

Secretary: E. Shilton, The Elms, Odds Farm, Green Common Lane, Wooburn Com- 
mon, High Wycombe, Bucks. 

Meetings: Monthly. 

228 



ASTRONOMICAL SOCIETIES IN GREAT BRITAIN 

Solent Amateur Astronomers 

Secretary: K. W. Arbour, 14 Orchard Avenue, Bishopstoke, Eastleigh, Hants. 

Meetings: Room 33, Library Block, Southampton University. 3rd Thur. each month 

7.30 p.m. 
Southampton Astronomical Society 

Secretary: J. G. Thompson, 4 Heathfield, Dibden Purlieu, Southampton. 

Meetings: 2nd Thur. each month Unigate Conference Room, Southampton; 4th Thur 

each month Room 33, University of Southampton. 
South Downs Astronomical Society 

Secretary: Mrs Buss, 32 Birdham Close, Stroud Green, Bognor Regis. 

Meetings: Last Friday in each month. 
South-East Essex Astronomical Society 

Secretary: P. A. Laycock, 42 First Avenue, Westcliff-on-Sea, Essex SSO 8HR. 

Meetings: Lecture Theatre, Central Library, Victoria Avenue, Southend-on-Sea. Gen- 
erally 1st Thurs. in month, Sept.-May. 
South-East Kent Astronomical Society 

Secretary: P. Andrew, 30 Reach Close, St Margaret's Bay, nr Dover. 

Meetings: Monthly. 
South Lincolnshire Astronomical & Geophysical Society 

Secretary: F. F. Bermingham, 19 Field Close, Gosberton, Spalding, Lines. 

Meetings: South Holland Centre, Spalding. 1st Monday each month, 7.30 p.m. 
Southport Astronomical Society 

Secretary: Howard Bloch, 4 Warren Green, Formby, Merseyside. 

Meetings: Saturday evenings, monthly as arranged. 
South Shields Astronomical Society 

Secretary: H. Haysham, Marine and Technical College, St George's Ave., South 

Shields, Co. Durham. 

Meetings: Marine and Technical College. Each Thurs., 7.30 p.m. 
South West Herts Astronomical Society 

Secretary: G. J. B. Phillips, 32 Riverford Close, Harpenden, Herts. 

Meetings: Royal Masonic School for Girls, Rickmansworth. Last Fri. each month, 

Sept.-May. 
Stoke-on-Trent Astronomical Society 

Secretary: M. Pace, Sundale, Dunnocksfold Road, Alsager, Stoke. 

Meetings: Cartwright House, Broad Street, Hanley. Monthly. 
Swansea Astronomical Society 

Secretary: C. Morris, 14 Bath Villas, Morriston, Swansea SA6 7AN. 

Meetings: As arranged. 
Thames Valley Astronomical Group 

Secretary: K. J. Pallet, 82a Tennyson Street, South Lambeth, London, SW8 3TH. 

Meetings: Irregular. 
Thanet Amateur Astronomical Society 

Secretary: P. F. Jordan, 85 Crescent Road, Ramsgate. 

Meetings: Hilderstone House, Broadstairs Kent. Monthly. 
Torbay Astronomical Society 

Secretary: Miss A. Longman, 4 Heath Rise, Brixham, Devon. 

Meetings: Quay Tor Hotel, Scarborough Road, Torquay. Monthly 
Waltham Forest & District Junior Astronomy Club 

Secretary: B. Crawford, 24 Fulbourne Road, Walthamstow, London E 17. 

Meetings: 24 Fulbourne Road, Walthamstow, London E.17. Fortnightly (Mondays) 
Warrington Astronomical Society 

Secretary: B. P. Rees, 2 Dale Avenue, Appleton, Warrington. 

Meetings: Central Library, Museum Street, Warrington, Lanes. Monthly, Sept.-May 
Warwickshire Astronomical Society 

Secretary: R. D. Wood, 20 Humber Road, Coventry, Warwickshire. 

Meetings: 20 Humber Road, Coventry. Each Tuesday. 
Webb Society 

Secretary: E. Moore, 7 Elvendon Road, Palmers Green, London, N.13. 

Meetings: As arranged. 
Wessex Astronomical Group 

Secretary: Mrs J. Broadbank, 624 Ringwood Road, Parkstone, Poole, Dorset. 

Meetings: Science Block B, Lower Annex, Poole Technical College. 



229 



1978 YEARBOOK OF ASTRONOMY 

West of London Astronomical Society 

Secretary: R. A. Hedley, 96 Warden Avenue, Rayners Lane, Harrow, Middlesex, HA2 

9LW. 

Meetings: Monthly, alternately at Hillingdon and North Harrow. Second Monday of 

the month, except August. 
West Yorkshire Astronomical Society 

Secretary: J. A. Roberts, 76 Katrina Grove, Purston, Pontefract, Yorks, WF7 5LW. 

Meetings: The Barn, 4 The Butts, Back Northgate, Pontefract. Every Tues., 7 p.m. 
Wolverhampton Astronomical Society 

Secretary: M. Astley, Garwick, 8 Holme Mill, Fordhouses, Wolverhampton. 

Meetings: Polytechnic, Wulfruna Street, Wolverhampton. Alternate Mon., Sept.- 

April. 
Wyvern Astronomical Society 

Secretary: A. F. Edwards, 2 Howcroft, Churchdown, Gloucester. 

Meetings: Clubhouse, Churcham. Last Friday of each month except Aug. 
York Astronomical Society 

Secretary: Mrs J. Acton, 1 Low Catton Road, Stamford Bridge, York. 

Meetings: York Railway Institute. Fortnightly, Fridays. 
Zenith Astronomical Society 

Secretary: A. Harvey, 10 Meadow Close, Reedby, nr Burnley. 

Meetings: 54 Cromwell Street, Burnley. 1st Wednesday in each month. 

It is possible that this list of local societies may not be quite 
complete. If any have been omitted, or any details need to be 
updated, the secretaries concerned are invited to write to the 
Editor (c/ o Messrs Sidgwick & Jackson (Publishers), Ltd, 1 
Tavistock Chambers, Bloomsbury Way, London WC1), so 
that the relevant notes may be included in the 1979 Yearbook. 



230 



The Editor 

Patrick Moore, O.B.E., was born in 1923 in 
Pinner, Middlesex. In the Second World War 
he served as an officer in the Royal Air Force, 
flying as a navigator in Bomber Command. 
He spent many years at East Grinstead, 
Sussex; was Director of the Armagh 
Planetarium (Northern Ireland), 1965-68. 
Following that he moved to Selsey and 
now has his own private observatory 
with a 15-inch reflector as the main tele- 
scope. His mam astronomical interests are 
the Moon and the Planets. He is a member 
of the International Astronomical Union, 
and a Fellow of the Royal Astronomical 
Society. He has recently been presented 
with the Jackson-Gwilt Medal by the R.A.S. 
His O.B.E. was awarded in 1967. He is 
currently Vice-President of the British 
Astronomical Association, 



cloth 283 98392 2 £4.50 
paper 283 98393 £2.25 



Photograph of Patrick Moore :■ 

copyright Mitchell Beazley Marketing Limited 1977 



Sidgwick & Jackson Limited 

1 Tavistock Chambers, Bloomsbury Way 

London WC1A 2SG 



to 

The Press on previous Yearbooks ... oo 

•< 

. . .worthwhile reading not just for the m 

active amateur astronomer but for anyone ^ 

with an interest in the nature of the *§ 

Universe . . . Patrick Moore at his best' g 

NEW SCIENTIST Q 

'Its success is partly attributable to the q 

convenience of having a practically useful -n 

set of star charts and monthly notes ^ 

combined in a single volume, with articles (/> 

of a popular nature on topics of -H 

astronomical interest' 2 

o 

THE TIMES EDUCATIONAL SUPPLEMENT ^ 

o 

'This unique handbook is an eagerly ^ 

awaited annual reference work for all ^ 

observers of the night sky. . . 

EAST ANGLIAN DAILY TIMES 

'Anyone who is interested in astronomy 

will find this book an invaluable addition " 

to his library' S 

THE OXFORD UNIVERSITY SCIENTIFIC SOCIETY 2 

'More than a mine of information' 

MORNING TELEGRAPH, SHEFFIELD tn 

A thoroughly expert diary' o 

LIVERPOOL DAILY POST J 

I 



5